I just submitted a bug report a few minutes ago, using Opera Mini 7.6 on Android, and I had the same problem as you.

After filling in all the fields, I clicked submit the first time, but nothing seemed to happen. I was simply taken to the top of the report wizard page I had completed (and, if I remember correctly, a message about not all fields being filled).

I then clicked submit the second time (and I believe I added my exact phone model after the word "Android", which had been pre-filled in the "Specify which phone and model you have").

At this point, it finally submitted correctly, and I received a page with:

"Opera Mini bug report wizard
Your bug report has been posted

If you would like to update your report with more information, please send an email to [email address]

You may wish to take a note of this address in case you need to refer to your bug report in the future

[.....etc ....etc]"