Because Mouse 4 is default to autorun what I suspect is happening is that bind is not clearing when you change it to be strafe. That is likely a bug and at this point should be reported as a bug. (You can do so on the bug report forums or in game on the support menu using the submit bug form.)
Given the steps some have already tried, I do not have any troubleshooting I could offer for this and my only recommendation is to not change that keybind from default and setup your strafe buttons to something different.
I do thank you all for providing those screenshots and hopefully with your bug reports this can get addressed by our QA/developers quickly.