This is a weird one. Opera offers extensive keyboard shortcuts and this may
interfere with your keyboard and how it is configured. This is only a guess and
I am not sure how or why, though. Since I can't replicate it, I am at a loss as
to how to get around it. I would start by looking at Tools| Preferences in
Opera, Advanced tab and Shortcuts in the list, using the mouse of course and
trying to delete shortcuts.

You could also try running Opera from the commandline. See:
http://www.opera.com/support/mastering/sysadmin/ and look at the switches here:
http://www.opera.com/docs/switches/

I notice that there is a keyboard debugging switch. Once you decide what works
then you can just edit your menu to reflect the launch command for Opera.