When I used the basic user registration package the emails worked once Jason had helped add the -f switch.
the problem only started when I purchased UE4 and added upload fields. In the server behaviours was a red exclamation with the message "old version" .
On the forum Iwas advises to double click which I did and the exclamation mark dissapeared. I then used UE4 to setup the uploads.
Since then no validation emails have been received. On the forum I saw other with a similar issue so tried it with my .me.com account and validation was received.
At that point I decided to plead insanity ;-)
As to your filling the form in, in my tests I can see I've filled it in 82 times with a sucessfull submission to the database. However since adding the upload no .co.uk emails are received - cant say about any others I have not tried.
I've attached two screen dumps of what I fill in to test.
I've also registered from PC's other than mine in case mine was throwing a wobbly
really sorry to be a pain but I do not know whats left to try.