Problem is not that it stops when a monster enters visual range, that has been the case forever and it's a good feature.
Problem is that you can't w5 your way forward from there. Not even a single turn passes, not to mention allowing it to come next to you, like it has been previously. Previously the sequence has been w5 -> monster enters LoS, turns cease to pass -> w5 again -> turns pass until another monster enters LoS or first monster gets adjacent. Now it's w5 -> monster enters LoS, turns cease to pass -> w5 again -> nothing happens.
It makes things like resting up and live saccing much more tedious and also more dangerous, as the feasible way to circumvent it is to hold down 5.
I'll re-check ToEF and add a savefile if I reproduce it.
EDIT: Looks like ToEF in general allows w5'ing, but on the temple level there seems to be something that constantly interrupts it. In the attached savefile (Flip.zip) only 1-2 turns elapse for each attempt, and I can't tell what the reason for that is.