[OS X][REG 5.4->5.5]: Moving a floating toolbar around will show it without the buttons rendered

[OS X][REG 5.4->5.5]: Moving a floating toolbar around will show it without the buttons rendered. Using the application example, just drag the toolbar around and then the buttons will no longer be rendered until the drag is finished.

This appears to have been introduced by 2ca1253b13e77643b3d2dd993a038ae2df882311 in qtbase