In theory these flags should be clearing when going from Standby to Rx.  What I found in practice was that they were not.  The very first packet I tried to receive was always corrupted, and while I was in receive mode but before receiving any packet, I still saw two FIFO bits set.  Writing this bit in my initialization solved the problem.  I think for the couple of bytes that this would add to the size of the library, it would be better to be safe than sorry to include it in yours as well.