So I have an HTC ONE M8 and everytime I connect it to my RC for my P3P it begins to charge of the remote controllers battery. This means the battery of the RC drains alot quicker and it maybe isnt too good for its battery either.
Firstly is it meant to do this?
And is this happening to just my phone or are other android phones doing this?
And I have tried switching the mode on my phone from charging to file transfer but it still keeps charging no matter what mode.

There is no charging going on when you connect, you see the charging icon because it is connected to a powered device.
This is normal.