Is that the filter on the lower left bottom of the picture? What is the clearance between the filter and the door when it is shut?

This not not usual an a bad installation. This probably done because there was not enough clearance to connect the duct to the grille. You may be able to solve this problem by installing a door with a lattice and removing the duct to no where.

This is the kind of non sense that occurs when a builder follows this:

"The HVAC equipment & duct work should not be in the attic, it should be in the conditioned space of the building."

Then the architect draws something up, not knowing HVAC doesn't give enough room to do the job properly.

So essentially the HVAC contractor was forced to turn that closet into an air return for your HVAC system. The only reason this passes code is that the heating portion of the system is not gas or oil system.

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That being said, you're not buying a 'normal home' -- you're buying a condo apt.

If to the lower left of the photo is the air filter... the bigger question is how much air can get to it once you close the door to that closet?