this actually works, probably just not what you intended?
FLIP is a special variable that has its own state. it doesnāt flip the state of the var/etc itās assigned to (in this case PN 0 4)
so if you execute PN 0 4 FLIP several times, indeed the fifth element of pattern 0 will switch from 0 to 1 to 0 each time.
if you want to simply invert the step, use:
PN 0 4 EZ PN 0 4