Sometimes our productive MySQL Server has many locked tables in the "show processlist". These locked tables get never unlocked, they were still locked after a few hours.
MySQL-Server 5.5, Debian Squeezy, MyISAM... The table which were locked and never gets unlocked has ~200 Inserts per minute at peak and 2 Inserts per minute normaly.
Why does MySQL not unlock the table? In which situation it can happen?