Universal Plugin Manager Disables Greenhopper after maintenance expiration

After the expiration of our jira/greenhopper maintenance period, the greenhopper plugin is not activated anymore.
The problem is reproducible and linked to the UPM bug described here: GHS-4887.
Unlike the systems described in the afore mentioned ticket, our system was already at versions:
Jira: 5.0.2
Greenhopper: 5.9.3
UPM: 2.1.1
(we had just upgraded everything on the 02. of april)
So there should not have been any issue with Greenhopper falling out of service on the 12. of april at 16oo when our maintenance contract expired.
The error i see when i start jira is
"com.atlassian.extras.common.LicenseException: You cannot update to GreenHopper version 5.9.3. Updates are no longer available." --> this version was already activated prior to the expiration of the maintenance period.
I have already tried to upgrade the UPM to 2.1.2 and Greenhopper to 5.9.4, each separately and in all constellations together (virtual machine snapshots be thanked), but to no avail. After contacting our atlassian representative, who confirmed that there should be no issue with out licences, I am posting this as a bug.
Anyone have any similar issues?