B3 may not be a good choice for the second sensor. As the Dusk Dawn address for the B2 sensor is B3.
Dusk/Dawn Address = Sensor Address +1.
I disabled a Dusk/Dawn function with electrical tape inside.. also I tried with B2 and B11 and a saem problem !!!
Another thing that maybe a problem. If both detect motion at the sametime. One may get through to the CM15A and by default after a detect the sensor waits; I believe 10 seconds; before it can again detect a motion. So no more detects will happen until the timeout is over.
I tought to hide one after other to hide a face, and verify a delay ... and always first is fast than a second !
I tried also to use B2 and C2 (B2 with CM15A) and (C2 with TM751)...
Maybe that a second is fail ... I will use this one to another place and buy another !