Backup and restore

I'm trying to find out if the following is an anomaly in this environment or if this is a bigger issue within Moodle. I have a course that is used for template purposes and therefore often used with the import function. After a migration to a new server and database the backup/restore function does not work on this particular course, neither does the import function as it relies on the backup process.

After the database migration I redefined defaults using the XMLDB editor's tools to check for defaults and keys and executed those queries. This might be important.

The debug log says the following. And the 'controller' contains 92364 characters. While it's database field is of the TYPE notation and therefore only allows 65535 characters.

Debug info: Data too long for column 'controller' at row 1
INSERT
 INTO mdl_backup_controllers 
(backupid,operation,type,itemid,format,interactive,purpose,userid,status,execution,executiontime,checksum,controller,timecreated,timemodified)

I'm now trying to find out whether this is an anomaly for this site; or a bug. I can circumvent the problem by making the 'controller' field in the database a LONGTEXT using:

ALTER TABLE mdl_backup_controllers MODIFY COLUMN controller LONGTEXT NOT NULL;

What is the controller's function?

How can a controller be so long?

Have you encountered this before?