Not to be overlooking the obvious - We have an ASCN and most of our hunt groups have a setup like this. Usually when it doesn't work, it is because of one of four things:
The hunt group in A is not advertised; the user has their DND on and doesn't realize it; they used a programmed button to log out of the hunt group and don't realize it; or they set up a call forwarding to another extension and hunt group calls are not forwarding. We've been doing this for some time with no problems, on both 4.1 and 4.2 - we are currently at 4.2.14.