@sierdzio and @jsulm Thank you both for the suggestions. I will work on number 4 with moving of tempfiles or using a QSaveFile.

@kshegunov I didn't know that function. Thank you very much, I will try it.

The bug was solved in Qt 5.8 so a while ago. I'll mark the thread as solved as well

I have quickly gone through existing bugs reported for QTemporaryFile and nothing related found. So I have created new bug: https://bugreports.qt.io/browse/QTBUG-46156. IMO its better to have a few duplicates, that not reported at all :) BTW, the resize(0) works fine.