I found the following on the opera website. Not official, but in their forums. let me know if it works.
Notifications bug WORKAROUND
Admins: Please remove if this violates the policies of this forum. If so, my apologies.
Here are they steps I've done to work around the Notifications being disabled. This allowed me to avoid removing Opera from my phone. I just couldn't bear to remove it as it's head and shoulders above IE for browsing! It makes it a simple matter to fix the notifications settings with only 2 clicks after closing Opera Mobile 9.5b1. Hopefully we will not need this workaround very long.
disclaimer - only use this procedure if you are comfortable with editing the registry as a wrong move could render your pda dead.
Download and install Fdcsoft Task Manager (free app)
http://www.dotfred.net/TaskMgr.htm
(before proceeding, make sure your notification settings are the way you want them as this will save them however they are at the moment)
Open Fdcsoft Task Manager (it gets installed in a folder under programs called "system")
1. click on the down arrow in the top/right of the screen and choose "regedit"
2. expand the registry to the following
3. HKEY_CURRENT_USER\Control Panel
4. TAP and HOLD on "Notifications" and click "Export"
5. navigate to \windows\start menu (so Start Menu is highlighted)(leave the default name of "notifications.reg")
6. click the bottom left icon and choose "associate ... " this will allow double clicking .reg files and having them added to the registry
Now after you open and close Opera Mobile 9.5b1, just go to the start menu and click "notifications" and you're settings will be restored.
Please post your results (were you able to work the procedure and are you still using Opera as a result?)