Steps to reproduce:
1) Start attached QMBox example application in portrait mode -> Application main window opens in maximized mode.
2) Tap "dialog without softkeys" -> Opens a fullscreen dialog without softkeys as child.
3) Tap "Switch" button once -> Changes the dialog to maximized.

Observe parent dialog softkeys peeking through, though faded. "Exit" softkey still works, though.

Note that if the child dialog is initially maximized, it will correctly get empty softkeys. This problem only manifests if the dialog is initially fullscreen and later changed to maximized, which seems like a somewhat rare use case.