This is throwing more fuel to the fire, but some posts make me wonder if they are not also picking the cards with more money:
Here
https://bitcointalk.org/index.php?topic=254533.msg8526281#msg8526281 a member says only his card with about 500 euros was blocked, not the others with very low quantities.
Since Mbank has his website in several languages and, if I recall correctly, there is nothing in the its agreement saying anything against foreigners buying its cards, I also can't see any ground for them to screw the foreigners and ask them to come to Poland.
It's not very different from a situation where a Bank closes all his branches in the USA, except on Florida, freezes all cards, and says to its customers: if you want your money you all have to come to Florida.