Branch 1342632: Calling user_save() causes user to be kicked out of all OG groups

Just going to throw this out there, I may be totally wrong:

Could it have to do with the fact that the field_data_og_group_ref table never gets populated with records when I add users to groups? I've always wondered why that table remains empty no matter how many user-to-group and node-to-group associations I have in the system, even though they are all using the og_group_ref field. In Views, for example, I've tried using og_group_ref to figure out group membership relationships but they never work because that table remains empty. Instead, I've had to rely solely on the og_membership table to determine these associations.

Perhaps during user_save(), the contents of field_data_og_group_ref are getting enumerated, and being that it's totally empty, it assumes that user is not a member of any groups and updates the contents of the og_membership table accordingly? Just a thought...

Okay, trying to reproduce it on a fresh install... so far no luck here, either! Will post another update soon as I find anything out.

To anyone who needs help with this, I think I managed to fix it. I uninstalled OG and entityreference completely (which involves deleting any OG-related fields from all entities), deleted the module directories, inspected the database and removed any leftover remnants of OG and ER that I could find (including tables, field definitions, and whatever else - there were a few bits here and there), cleared the cache, then "git clone"d the OG and ER branches again, re-enabled the modules, and recreated the group properties on my entities. I am no longer getting these weird errors when a non-admin user that is a member of groups logs in.
Edit: this is irrelevant now... see ticket description.

Actually... I spoke too soon! It is totally still happening - I just hadn't logged in again for a while. Sigh... Narrowing down the problem... will post an update soon!
See issue description.

Gosh.. never mind. I finally found the source of the errors. It's a module I've written. Must be written poorly. Really sorry for the hassle, @Amitaibu!
See issue description.

I've narrowed down this problem further. I believe my module is written properly. What my module does is very simple. It hooks into hook_user_login(), tweaks one or two fields on the user account that is being logged in (basically syncing some fields from a remote service), then saves the user object using user_save(). In fact, not even changing any fields at all on the account, but simply re-saving the global $user object causes this slew of errors (and the user gets kicked out of all groups they were a member of).

See if it happens for you:

function mymodule_user_login(&$edit, $account) {
  $account = user_save($account, array());
}

Hiding confidential information from summary

Okay. Well I've just worked around it for now by using direct SQL queries to update user records. When I have more time again I'll try to come up with a comprehensive step-by-step procedure to reproduce this!