Yes, that's the reason although it wasn't a forgotten temporary thing. For the majority of communities (even huge ones) they don't typically have enough members to get near the limit of MEDIUMINT and it wasn't worthwhile forcing a large number of database changes for those that wouldn't be affected.
We've got an internal issue for this so we'll make it easier to change these columns when appropriate.
For @David.. as a temporary work around, if you find the lines in the file @teraßyte mentioned ( /system/Application/Application.php on line 2846), temporarily delete the following and then go to the support page in the AdminCP.
if ( isset( $differences['type'] ) and ( $differences['type']['is'] == 'MEDIUMINT' or $differences['type']['is'] == 'INT' ) and $differences['type']['shouldBe'] == 'BIGINT' )
{
unset( $differences['type'] );
if ( isset( $differences['length'] ) )
{
unset( $differences['length'] );
}
if ( isset( $differences['unsigned'] ) and !$differences['unsigned']['is'] and $differences['unsigned']['shouldBe'] )
{
unset( $differences['unsigned'] );
}
}
When you're done running the queries it presents, you can restore that file back to default. As always, it's a good idea to make sure you have a good database backup before making changes to the structure.