Regression: UI drawn like disabled when window is not active

When switching away from a Qt5 window (making a different window/app active), all "stock" controls, labels and other widgets are drawn with a grayish, disabled look.
This

a) is a huge behavior change to Qt4, e.g. breaking the style in combination with custom widgets
b) breaks with the style of all native applications that I looked at, i.e. no other application that I found did that

See the attached screenshots