I wouldn't have described it as master and multiple…just two independent delays.
If tempo *is not* turned on, tapping the delay in sets A and B to the same time (ms)…seems to be a bit of a limitation but I can't think of a different and consistent behaviour.
If tempo *is* turned on, your independent A & B subdivisions are preserved in relation to the new tempo…which is what you seem to want
I barely ever use the unit without tempo being ON.
Hope I've understood your problem there.
Edit: that's pretty much what Roobin said…bit of a posting-delay going on here! 😉