I have seen generic filters do this. Be sure to use original Miele filters. The generics are a few dollars cheaper to buy but you end up with an inferior quality filter that could cause other problems by continued use. same is true with bags.
A clogged filter may also do this. Miele vacuums are very tightly sealed, the exhaust air has to come out. If the filter is clogged, the pressure could pop the filter out, HEPA filters are suggested to change out about every 50 hours, for most people this is between 1 - 1.5 years.
We had a Miele come in for service the other day with the same complaint, installed filter was a generic, customer said it was a new filter just installed. We replaced with an original filter and problem ceased.
If you need any help feel free to contact me.