I'm having a problem now that's just manifested itself, where people's Photobucket pictures are getting .html appended to the URL. Apparently no one else is suffering from this problem.
I'm getting that too, with Opera 12.14. Haven't tried it with a spoofed User-Agent, though.
There are threads on the Opera forum about it. It appears to be a real problem with Opera. Users report having submitted bug reports, both to Opera and to Photobucket, although Photobucket doesn't officially support Opera. I've tried everything I can think of that I can tweak in the preferences, whether site-specific or global, including scripting, plug-ins, redirection, referral, browser ID. Nothing has worked.
Opera's upgrading their render engine soon, so an important upgrade is coming soon, if not a major one. Maybe it'll get fixed then.
I'm not happy!