I use mouse4 for +speed and it will just not work. Can bind mouse4 to +movedown and it works perfect for crouching.

I've tried changing mouse4 function to a keystroke "shift" and this also does not work (worked fine in standalone version of quake)

I have uninstalled quake and reinstalled and used shift on keyboard and it will work for +speed until i use the mouse key which is bound to speed and then it no longer works on keyboard either. Have played quake for years with the same setup and never had an issue. hopefully they will fix the bug.