When working my Heidi on a remote server which is a master in a multiple master replication environment, I have to take care, when using the user manager, that I first select a database, which is not replicated, otherwise the "RENAME USER ..." (for example) is replicated on the salve, which mostly breaks the replication, because masters and slave generally have different users.
The simple solution would be to execute a "use mysql" before the user manager is doing changes.
Thanks in advance.