According to this:
http://www.lotnisko-chopina.pl/en/ai...chopin-airport
MCT for longhaul ->Schengen connection with LO at WAW is 35 minutes. So your 50 minutes are OK. Had a similar connection this summer. Our flight from ORD was late, so it looked like we will miss our connection to RZE. LO agents escorted us trough immigration and Schengen security in order to make our connection. We made it.