Although, it may still show GM2, a quick check of the MTO database will indicate that your M2 has indeed expired. I expect if you show up at a Service Ontario looking to book a M road test, you will be advised it was indeed an error and you will have to start over as an M1 licencee.
Civil servants, (or more correctly in Service Ontario, contracted employees), OFTEN make mistakes. Just because an error has occurred, doesn't mean it goes in your favor, (just like the banks if they screw up and deposit $1 million in your account you do NOT get to keep the money).
If the funds, (or any part thereof), are missing when they attempt to recover it, one is subjected to a charge of theft, (over or under depends on if the amount missing exceeds $5,000 or not...lol
Also, if your currently riding, and happened to get involved in a collision, and the insurer discovers your riding in essence without a valid licence they "could" refuse the claim. Now, at some point, some court "may" rule that it was an "honest error", but that would take YEARS, to straighten out, in which time you have been bankrupted, and destroyed financially.