Actually, as I read it, it makes quite a bit of sense. If you keep the residence where you were recruited and it's in a PLDA, you will not get PLD for that residence if you are prohibited posted elsewhere because that is where you were recruited. Now, if you and your family were posted to Area A, which is in a PLDA, and then you were prohibited posted to Area B, you would still get PLD for Area A because it is in a location away from where you were recruited.
The point of PLD is to provide a bit of help to offset the costs of living in an area WHERE THE CF POSTED YOU. If you still have a residence in the area where you were recruited, the CF didn't send you there. That's where you started so why should they give you extra money?
Now, if you were to finish all your training and then the CF were to post you to the area which happens to be where you were recruited, you would likely be eligible for PLD.