This happens quite randomly. Sometimes it works; sometimes it doesn't as shown on the screen shots. With the code that I'm including in this message, it doesn't work most of the time, meaning the tiles get stuck on the left as it loads, when it's supposed to spread out evenly.

When I remove all the xamcharts, lays itself out correctly 100% of the time. but that's not acceptable because we need the charts.

When I remove the xamGrid, it also works 100% of the time. That's also unacceptable because we need that grid in the application.

Figure 1. Tiles bunched up on the left (BAD)
 

Figure 2. Tiles spread out evenly (GOOD)

Here’s the XAML code:
(Obviously, our application is more complex. I’ve simplified it as much as possible for the purpose of troubleshooting)

<UserControl x:Class="SilverlightTiles.MainPage"

    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"

    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"

    mc:Ignorable="d"

    d:DesignHeight="300" d:DesignWidth="400" xmlns:ig="http://schemas.infragistics.com/xaml">

    <Grid x:Name="LayoutRoot">

        <ig:XamDockManager x:Name="xamDockManager" >

            <ig:XamDockManager.Content>

                <ig:DocumentContentHost Orientation="Vertical">

                    <ig:DocumentContentHost.Panes >

                        <ig:TabGroupPane>

                            <ig:ContentPane x:Name="FirstPane"

                                            Header="First Pane"

                                            IsActivePane="True"

                                            IsDocumentPane="True"

                                            AllowClose="False"

                                            FontSize="14">

                                <Grid x:Name="TSActivitySummaryGrid">

                                    <Grid.ColumnDefinitions>

                                        <ColumnDefinition Width="300"></ColumnDefinition>

                                        <ColumnDefinition Width="*"></ColumnDefinition>

                                    </Grid.ColumnDefinitions>

                                    <ig:XamGrid Name="xamGrid1"></ig:XamGrid>

                                    <ig:XamTileManager Name="xamTileViewSummary"

                                                       VerticalAlignment="Top"

                                                       Grid.Column="1" >

                                        <ig:XamTileManager.MaximizedModeSettings>

                                            <ig:MaximizedModeSettings

                                                MaximizedTileLocation="Top"

                                                ShowAllMinimizedTiles="True"

                                                MinimizedTileExpansionMode="AllowOne"/>

                                        </ig:XamTileManager.MaximizedModeSettings>

                                        <ig:XamTileManager.NormalModeSettings>

                                            <ig:NormalModeSettings ShowAllTiles="True"

                                                                   TileLayoutOrder="UseExplicitRowColumnOnTile"

                                                                   MaxColumns="3"

                                                                   MaxRows="2"

                                                                   VerticalTileAreaAlignment="Stretch"

                                                                   HorizontalTileAreaAlignment="Stretch"

                                                                   MinColumns="3"

                                                                   MinRows="2" />

                                        </ig:XamTileManager.NormalModeSettings>

                                        <ig:XamTile  Header="Un"

                                                     ig:XamTileManager.Column="0"

                                                     ig:XamTileManager.Row="0">

                                                <ig:XamDataChart x:Name="SampleChart1">

                                                </ig:XamDataChart>

                                        </ig:XamTile >

                                        <ig:XamTile  Header="Deux"

                                                     ig:XamTileManager.Column="1"

                                                     ig:XamTileManager.Row="0">

                                            <ig:XamDataChart x:Name="SampleChart2">

                                            </ig:XamDataChart>

                                        </ig:XamTile >

                                        <ig:XamTile  Header="Troix"

                                                     ig:XamTileManager.Column="2"

                                                     ig:XamTileManager.Row="0">

                                            <ig:XamDataChart x:Name="SampleChart3">

                                            </ig:XamDataChart>

                                        </ig:XamTile >

                                        <ig:XamTile  Header="Quatre"

                                                     ig:XamTileManager.Column="0"

                                                     ig:XamTileManager.Row="1">

                                            <ig:XamDataChart x:Name="SampleChart4">

                                            </ig:XamDataChart>

                                        </ig:XamTile >

                                        <ig:XamTile  Header="Cinq"

                                                     ig:XamTileManager.Column="1"

                                                     ig:XamTileManager.Row="1">

                                            <ig:XamDataChart x:Name="SampleChart5">

                                            </ig:XamDataChart>

                                        </ig:XamTile >

                                        <ig:XamTile  Header="Six"

                                                     ig:XamTileManager.Column="2"

                                                     ig:XamTileManager.Row="1">

                                            <ig:XamDataChart x:Name="SampleChart6">

                                            </ig:XamDataChart>

                                        </ig:XamTile >

                                    </ig:XamTileManager>

                                </Grid>

                            </ig:ContentPane>

                        </ig:TabGroupPane>

                    </ig:DocumentContentHost.Panes>

                </ig:DocumentContentHost>

            </ig:XamDockManager.Content>

        </ig:XamDockManager>

    </Grid>

</UserControl>