Haha, well, I had the same funny experience trying to get into the Metro putting my ticket on the right and the door not opening...  Good for me it was all empty and the lady from the ticket booth made me know it's the other door... I can imagine if I had people queuing behind me ahhahaha, because this is how is it in my lovely country - you HAVE TO know, if you do not know it's your fault :) The good thing is our Bulgarian common sense is quite strong I would say :)

BTW, it's not the same at all the stations, is it? I recall some having the entrance built in the "expected" and "natural" way, right?