ArcMap 10.2 Does not cleanup aliases after a join

When you join a table to a featureclass the alias names get fully qualified prefixes, which is a good idea, especially for duplicate field names.

However when you remove the join, not all the aliases revert to unqualified, resulting in new commands failing to recognise the original fields. I tried closing the table and re-opening to no avail.

Workaround: Go into the properties and edit the alias by hand.