I guess you did not read my complete post.
I was offering a suggestion to diagnose the problem.

Not suggest a different theme to use.

I don't think it is a stock bug.
Other than it is a user induced bug.

You are using a non stock theme as well as custom html.
You need to eliminate both items.
Evaluate if the captcha is working as well as the other items.
Then proceed to add one variable at a time.

Currently you have to many items to eliminate out of the possibilities.

All of the stock themes have zero complaints on the issues you have.


Blue Man Group
There is no such thing as stupid questions. Just stupid answers