[Reg 5.10->5.11] Combo boxes rendered too far up

As you can see from the attached screen shots, in 5.11 combo boxes are drawn too far up, which results in badly looking layouts.

This affects Qt Creator (QTCREATORBUG-20801). Qt Designer is also affected in its property editor, though there one could say that it just exchanges one bad-looking layout by a differently bad-looking layout.