IP: 51.143.19.abc (mostly)
UA: standard bingbot UA with standard bingbot headers
I don't know if they are planning on making a habit of this. I first saw bingbot from 51.143 on 13 October, and more often in the last few days.
Tangentially, I didn't even realize 51.140-145 (i.e. 140/14 and 144/15) belonged to Microsoft. I've seen the range fairly often, but invariably used by malign robots who were blocked at the gate. This, on the other hand, shows every sign of being the legitimate bingbot: matching UA, matching headers--some of them fairly distinctive--matching habit of requesting nonexistent files thanks to getting their links garbled. No robots.txt requests as yet, but that isn't dispositive, since they're shared out among all their multifarious IPs.
It is, of course, possible that a maverick botrunner has hit on the trick of matching the bingbot's UA and headers, but there's nothing in the requests to raise suspicion. That is, no wp-admin, no xmlpr-whatsit and so on.
Hmm.
