Did it in mid June 14 from to ORD. ZED on AirBerlin to tegel and on to Krakow where we met up with our group one day after they revenued out. No issues.
Return was dicey but we never got stuck. Used my phone and myIDtrvl to change on fly. Flight from Krakow to Berlin was full so flew to Vienna on Austrian, but ORD was full so went Vienna to Dublin on Aer Lingus and on to ORD just barely though. Be prepared to get creative and maybe get stuck if you do this! Good Luck.