Vertical scrollbar in QTextBrowser scrolls to wrong location when lots of text was entered

In the open source VoIP client Mumble we have identified a bug in QTextBrowser that occurs after lots of HTML text has been entered.

The code

verticalScrollBar()>setValue(verticalScrollBar()>maximum());

stops working correctly after lots of text has been entered into the QTextBrowser. The scrollbar scrolls to some position (which is always the same position), but not the end of the widget as expected.

The downstream bug link is: https://github.com/mumble-voip/mumble/issues/2504 (the downstream bug is marked as closed, because there is nothing downstream can do about it)

The issue affects multiple users on different Qt versions, I have selected 5.14.1 because that is what I'm currently using.