Don't forget classes
Don't forget classes

Summary: Reading the code, I found that whenever a group got filled up, a class would get "lost" for no apparent reason. This is getting fixed here.

Reviewed By: beicy, Feng23

Differential Revision: D28423615

fbshipit-source-id: 81677cbeb650b35e3e021d5087d618b3307b8e9a

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