QFileDialog invisible (yet present)

Whenever the QFileDialog is displayed for any reason (open/save file(s)) and in any application, more than half of the time, the dialog remains invisible. However, everything behaves as if it is visible, i.e., the main application window is blocked (if modality is set) and I first have to press Escape to close the invisible QFileDialog before continuing. It doesn't happen all the time, and if it does happen, closing the invisible dialog with Escape and trying again may or may not work, it's pretty random. As mentioned, this happens with my own apps, as well as any other Qt app, it's not application specific.

This has happened for quite a while, even already with older version of Qt 5 (i.e., Qt 5.3.x and Qt 5.2.x) if I remember correctly (not sure how far back though)...

Steps to reproduce:
> Use any Qt app (e.g., okular, gwenview, ...)
> Attempt to open/save a file

Expected Behaviour:
> QFileDialog shows up

Observed behaviour (more than half the time):
> QFIleDialog is opened yet invisible