Looks if code changed to avoid send of shares below difficulty.  May be because of load on TML servers.  It would be excuse for not allowing connections from older client.

Bitstreams significantly differ, but could be result of compilation of minor change.  Appears some midstate java code calls simplified.  Could be reason for larger bitstream, to move into fpga.  Midstate changes relate to signcryption and could be server affecting as well.

I am guessing based on simple analysis of available source code and eyeball + tools of bitstreams.