QTextDocument generate contentsChanged just once after app start

I have a simple application with QTextEdit

And when I start application and when I click into QTextEdit, QTextEdit(QTextDocument) will emit

contentsChange and contentsChanged

this ony behave like this on Linux( ubuntu 20.04, 21.04) all fine on windows

It behavie like this only on first focus to QTextEdit

all other focuses are fine

contentChange emit with all removed and all added

Just start Example and click into one QTextEdit and on my systems I can see emit contentsChange  and contentsChanged