Code completion empty window

This is a regression, likely since qt (or qt-creator) 5.

When I open any drop-down menu in Qt creator (like code completion, or picking color scheme in Preferences), it is empty. Until I hover with mouse or use arrow keys. See the attached pictures:

• one after I pressed Ctrl+Space to show the code completion drop down menu,
• the other after I pressed the down key several times (few items are rendered).