Is it the 757 where cycling the flight directors takes you out of Approach mode?
On every 737NG I have flown it wouldn't work. When the F/D's go off the a/p goes into CWS pitch and roll, and when you bring the F/D's back the FMA's come back in VOR/LOC and G/S, you are exactly where you started, in Approach mode.
Is the NG the only Boeing that does this? If the 757 doesn't behave like this then I guess it's irrelevant to the topic and I'll drop it.
Cheers