RT5.0.1 removing a users email address

I am using RT5.0.1 and have a problem with RT removing an email address from a configured user. I Know this because looking at the history of the user it tells me

Fri Jan 14 10:00:00 2022 admin (Admin user) - EmailAddress changed from (no value) to ‘user@valid.email.address’
Mon Jan 17 11:10:02 2022 The RT System itself - EmailAddress changed from ‘user@valid.email.address’ to (no value)

If I put it back again it will be removed again. I do not know whats triggering the removal.

I can see no other errors that would indicate why the ‘System itself’ decided to remove the email address from this active user. This means the user does not get notified about tickets he is watching.

Whats causing the System to remove this valid email address and how can I fix it.

Do you have any custom scrips that might be running?

This is a stock install with no addons or custom scripts except for full text search enabled. It does run rt-clean-sessions and rt-fulltext-indexer out of cron.
It seems to be only happening with one particular user but there is nothing different I can see about this user or his email address.

After putting up with the problem for a weeks, I finally had time to try and diagnose the problem. I determined that the problem was occuring at login time. This was not originally apparent as many users dont log out. So I turned on debug logging and saw that its retrieving LDAP data and asking for a mail field called mailRoutingAddress:. The other fields did not have the : so removing this char and it fixed the problem.

This probably wont help anyone but at least its a resolution.