When you use the F5 keyboard shortcut to show or hide the Brushes panel, the currently selected layer is deleted. This issue occurs in Photoshop 14.1, not 14.0.
Temporarily reassign a different shortcut to hide/show the Brush panel until this issue is resolved. If you assign a different shortcut, make sure that you don't use the F5 shortcut before this issue is fixed.
You can use Undo to retrieve your layers, if appropriate.
Adobe is working on a solution for this issue.