Confusing bit of track work.

With just over a week to go, I decided to turn two of the fiddle yard roads to a depart/arrival line and a run arround loop. This will make things a bit easier at exhibitions, as the locomotives won't need to be handled so often which will reduce the chance of damage.
It worked fine when the point was set towards the depart/arrive road, but when the point is changed, it shorts the system.
So some investigation was needed. It turns out, Peco points are basically 'DCC friendly' the following diagram s show the two polarities in blue and red.
If the power is fed into the point via the turnout road, which it is on the fiddle yard, the polarity of the frogs and check rails are different to the rail that comes in.
I find it hard to discribe, but if you have a look under a point, you could see the two short pieces of wire joining 4bits of rail together.
All of this was done on my phone, so sorry about the poor quality!