Here is some code I use to apply an icon and tooltip to the cells
cell.ToolTipText = "sample text";
cell.Appearance.Image = Properties.Resources.Icon1.ToBitmap();
I use it to display notes related to some entities, so anytime the user wants to add a note, I update the icon if the type of note changes, and the tooltip also changes with the text of the latest note.
How are you applying the Appearance to the row? Usually, the best and most efficient way to apply any row-level settings like a tooltip or an appearance is to use the InitializeRow event.
If that's not helpful, then I recommend you make sure you get the latest Hot Fix. This might be a bug that has already been fixed.
If that doesn't help, then you should Submit an incident to Infragistics Developer Support an, if possible, include a small sample project demonstrating the problem so they can check it out.