How can this plugin be hanging?

[monotreme]

I have a hook on register_addmember_complete

It basically sets up some post variables of some vbulletin variables and posts them via curl to a proprietary script. very short script like plugin code is supposed to be.

I know for a fact that the proprietary script is not looping. I placed a log statement right before the end of it and it obviously got there because it wrote the notification to the log.

The behavior is this: whenever I register a user it enters them perfectly into vbulletin. It also does all the stuff my proprietery script tells it to do. It just doesn't ever return and give me the little blurp that vbulletin normally gives people when they register.

Any ideas?

The system on which it is failing is running php5. I commited the changes and updated them on a php4 system and it does NOT fail in this way...

OTOH it could be something else...