QColorDialog::ShowAlphaChannel infinitely expands dialog on OS X

Each time I create a QColorDialog on Mac OS X with the QColorDialog::ShowAlphaChannel option, I get a dialog that is slightly higher than the one below (probably the height of the alpha channel slider). It keeps on infinitely expanding until I quit the program. It doesn't matter whether I create this dialog using new QColorDialog, or using QColorDialog::getColor(), behavior is always the same with this option.

I can reproduce this by changing the widgets/scribble example, and changing the getColor call to pass in the QColorDialog::ShowAlphaChannel option.

I tried this using different versions of Qt on different machines running Mac OS X Yosemite (10.10.2). We also have several customers reporting this issue.

It feels like there's a problem with geometry restoring (e.g. it saves the geometry of the dialog with the slider, restores the geometry of the dialog but without the slider, then adds the slider, and then it grows with the height of the slider. But this is just guess work.