Sounds like the vacuum effect to me, too. If you've ever used a
high-end Sub-Zero or a commercial freezer, you'll find that the door is
MUCH more difficult (next to impossible in a commercial freezer) to
re-open immediately after closing. As you close it, you hear the air
flow, and the door pulls itself for the last inch or more. I'm not
positive what causes this, be it some sort of automatic pump or just
the existing thermodynamics, but it's definitely there, it's definitely
not caused by the magnets, and it sure appears to be an intended
effect, not a "well known problem".
I'm guessing that you didn't notice this right away on your fridge
because the effect is not as strong. I never noticed it in my own
Frigidaire until I started working in a commercial freezer, and then in
my employers' home Sub-Zeros. In my experience, the more powerful the
fridge or freezer, the more powerful the effect.