10.4 strange behaviour of cyrus reconstruct

Yesterday I did a reconstruct (from the command line using -r -f) of a user’s mailbox. After the reconstruct some of the IMAP mailboxes of this user could not be read (“mailbox does not exist”). Among those was the inbox.

It took me a lot of time to trace the cause, but eventually I found that after a reconstruct the username of the user was ‘spontaneously’ changed in the cyrus.header file. The username is all lowercase, but after the reconstruct either the first character or all of the username are uppercase. When I change them back by hand, the mailboxes are available again.

To illustrate this: Before the reconstruct the cyrus.header file reads:

———–
^B<8B>^MCyrus mailbox header
“The best thing about this system was that it had lots of goals.”
–Jim Morris on Andrew
user.username 65bad91a4283c246

username lrswipcda
———–

And after the reconstruct it may be changed to:

———–
^B<8B>^MCyrus mailbox header
“The best thing about this system was that it had lots of goals.”
–Jim Morris on Andrew
user.username 65bad91a4283c246

Username lrswipcda
———–

Now, I never have this behaviour with 10.3 (10.3.8 is the last version I have). The strange thing is that it is reproducable.

Does anyone recognize this behaviour and have an idea what is going on?