OK go into the key combinations and the key and its combinations that are set in persistent storage and the opera assosciated web/dev/app/extensions as such or may be
i find that to bulk delete cookies only restores any fault as soon as you close it in settings so set delete all when browsers closed then close then delete the few that are left.one at a time
this is the only real way where the alt key will keep being overidden by any of these and unfortunatley i doubt if u can have any alt set key on its own unless u find that small occasional compatible set up for all.i dont use any updated or any other than my orignal customised version of opera 36 and for occasional personal browsing other is 47 custom you can have a copy of the 47 if you ,like but the rest after 36 deliberatley remove these accessibly and go on doing so