M0/M1 in subroutine?

I'm about to start testing my M6 remap for an ATC and I'd like a bit more control while running through the sequence.  Single-block doesn't work for non-motion g-code lines.

Do M0 or M1 program stops work normally when inside a subroutine?

If not, is there an easy way to force a stop which requires a user input to proceed? 

As far as I know they behave normally in a sub. But I can't say as I've used them that way.. (It shouldn't take much to test.)

Thanks much - just wanted to confirm that they were known to not work properly.