Problem with user details being overwritten

[squishi]

I recently created three new extensions to my board. Additionally, my vbulletin forum is modded quite a bit (both in the source files and with custom plugins).

A couple of days ago, I noticed that the user details of my admin account (userid 1) were changed. Some userfields were overwritten. The avatar and profile pic were changed.
I discovered the same avatar and profile pic on a new member's profile. So he must have inadvertently changed my profile while editing his own profile.

I was not able to recreate the problem. I signed up with a new account, changed the user details of that account, but it did not have any effect on the admin account's details.

Say that for some reason, the user data gets saved with the userid "1" to the database. But then the guy would not be able to change his own info. It seems though as if his userdata was copied into my admin account.
I can't explain it. It is very worrysome.

I have three plugins that effect the signup process. I've looked at them multiple times, and cannot find a problem with it. And the user details are changed after the signup anyway.

The question is how I can debug this? I know on vbulletin.com I would just get the standard copy & repaste reply of pretty much reinstalling the forum from scratch. I am not going to do that.
Has anybody ever had such a problem before?