I have some 7945's that register to CUCM 8.5.x.
The reg fine and pc behind commicates without issue.
Strange thing is after a certain amount of time, the PC seems to lose connectivity after a few hours or few days.
The PC was and is fine without the 7945 inline.
Using Brocade FCX648_HPOE
Strange thing is I have 6941's working fine at that site and have replaced the 7945's with multiple new known working phones.