Is it only me that see's this..

Any time i have to remove copings on a roof that have a plastic dpc under them the plastic is wet.This is normaly due to the plastic sweating,basicaly making your own leak! This is on free stone and concrete ones.

I had to remove new concrete copings on a party wall on one house which had a dpc under them.At the bottom where the angled coping met the one flat one the dpc was folded back on its self.In this fold was a puddle of water,and all up the dpc it was covered in condensating water.

Whats the point,i mean its not as if water is going to come through 2" of a concrete coping.Then you see the edge of the dpc under the coping on other jobs.
The water tracks across the top and UNDER the dpc when it runs off the coping.

I rip the the plastic off and then bed them on a water proof sand cement mix.I suspose the people who use this practice dont ever go back to find out it causes more trouble than its worth.

Can not stand parapet walls i think they are pants.

Why not build a proper gable then roof OVER it, is what i say

I steer well clear of jobs that may involve them.

I have never seen the OP's problem, and don't agree that any parapet DPC contributes to a water ingress.

However, I was under the impression that using felt or suchlike as parapet DPC was no longer considered good practice as it allows the parapet or coping above it to debond from the wall below, crack, move and potentially fall away.

A DPC is required but alternatives to a roll of felt or polythene should be used in most circumstances

polythene dpc is poor practice, a lead tray correctly fitted is the way to go, mechanical ties are easily fitted to tie copings/bricks etc stopping any chance of failure/slippage..
bedding with waterproof muck is ok short term imho

a lot of copings dont have a proper water check bead under the front and back edge leading to water ingress plus a lot of water gets past the joints too..i normaly fit a 45mm grp black trim to the front edge and cap the whole coping allowing a drip edge 5-10mm to hang over the bottom back edge which falls onto roof in a nice brindle colourd pollyester mineral...looks nice and is a long term solution to damp walls above a flat roof