cannot delete user

[rolandm99]

hi,

i cannot delete a user.

# /opt/open-xchange/sbin/deleteuser -c 1 -A oxadmin -P ***** -i 6
user 6 in context 1 could not be deleted:
Server response:
ACC-0004 Category=8 Message=A SQL error occurred: Cannot delete or update a parent row: a foreign key constraint fails (`oxdatabase_6/pop3_storage_ids`, CONSTRAINT `pop3_storage_ids_ibfk_2` FOREIGN KEY (`cid`, `user`, `id`) REFERENCES `user_mail_account` (`cid`, `user`, `id`)). exceptionID=-1212246608-12


6.16.1

[rolandm99]

mhh, i dropped table pop3_storage_ids

mysql> DROP TABLE pop3_storage_ids;

and recreated it. now i can delete this user.
but why?

Roland