Well not really.
There should be a check valve between the vacuum supply and the holding tank to keep this from happening.
My check valve is in place but is bad and at times I can hear the air flow change where it is going.
So just because the valve is in the line check to make sure it is working.
And yes that tin can can also rust out and cause a vacuum leak, been there done that also.
Dave ----
With a leak the vacuum tank can only do so much. I had a small leak on the recirculating door plumbing on my Bronco and it would show up on long climbs in the mountains.
Had a big leak on my truck, hose knocked off by a mechanic, and it would catch up and go to vent, but any acceleration and it would go back to defrost.