Today's version of LyX 1.5 on a bang uptodate RH4 linux machine. Repro: Open the User Guide. Move the mouse over the foot note inset on the second line: by the LyX Team [foot]
Expected: the "foot" text does not move although the button background changes colour. Actual: the "foot" text moves 1 pixel down and to the left. On leaving the inset, the text moves back to its original position. This repros with all button insets, whether collapsible or not and whether or not the collapsible text is displayed. -- Angus