Try for example http://musicbrainz.org/release/add?artist=f468b272-235e-4d31-851a-a1d9859ac89a

Type any character into the Title field, and witness how the whole UI jumps upwards a bit and becomes obscured, so that one can't continue.

I work for Opera Software, so if you find that this is due to a bug in Opera or a workaround you made for Opera, please let me know and I'll look into it on our side too.