There are two reasons I can think of. One is that you hooked the event of the tab group which you initially put the pane into. However TabGroupPane and SplitPane are never moved so if you drag elsewhere the pane the panes will no longer be in that tabgrouppane/splitpane. The other reason would be if you're trying to hook that event at a higher level (e.g. on the xamDockManager) and expecting all tabgrouppanes to bubble up to that. Panes in a floating window are part of a separate WPF window and as such are not part of the event route that would contain the xamDockManager or other "docked" elements. Since SelectionChanged is a routed event you could hook the event on the ToolWindow in the ToolWindowLoaded event and then evaluate the e.OriginalSource to know what TabGroupPane (assuming it was a tabgrouppane as that event is raised by the WPF Selector class so it could be things within a pane).