Well I stand corrected yep I meant SR731 RF Repeaters, and I got at least ten of those slimline switches and it wouldn't repeat any of them!!! and I mean some of them where inches away funny it works fine will all my other remotes that's why I don't understand it's supositly the same signal I mean B2 on is B2 no matter what device is transmitting it isn't it
Whether or not the RF signal is recognized as a B2 by any receiver will depend on the transmitter's carrier frequency and pulse timing being within the range of what the receiver expects. If the receiver has a narrow bandwidth and the transmitter's carrier frequency is sufficiently different, or if the pulse timing is sufficiently different than the receiver is looking for, then the B2 signal may well be ignored or rejected as noise.
It's also possible that X-10 took some shortcuts with the actual pulse train transmitted by some versions of the Slimline switches but neglected to verify that the shortcut worked with the SR731.
One would have to check both good and bad receiver/transmitter combinations using RF measuring equipment to really understand what's going on.