Nota bene: Filter Connection ( www.2filter.com ) warns about screwing a wide angle adapter into a thin polarizer, and I have heard of several people who tried that and had the hardest time separating the polarizer from the adapter afterward. It is tempting to try to save on buying an $80.00 105mm adapter ring and a $320.00 105 mm CPL. Don't mate a modern CPL by its female threads. The only use female threads of a CPL should have is to serve as lens cap holder.
I had this problem with a Lee WA adapter and my B+W CP-L. When I was using it, it felt great that I could use the two and also turn the polarizer merely by turning the Lee system altogether clockwise.
However, I realized to my dismay afterwards that the outer ring of the CP-L, which I need to grab tightly in order to get the WA adapter off, is completely hidden under the adapter. Turning the adapter counterclockwise merely turns the outer ring of the polarizer with respect to the inner ring, with no effect on removing the adapter whatsoever.
The solution was to use gaffer's tape to secure the two rings of the polarizer and then twist them off as one piece.
You can have a similar situation with a regular filter if you screw the adapter on too tight.
I can understand it might worry some to have the lens 'bare' while using the Lee system, especially as you carry the camera+lens from one place to another, because you wouldn't have the filters stuck at that time, and you might not want to take the adapter on and off every time to put the lens cap on. I recommend getting the Lee filter caps ($ 8 for 3 pieces) and ensuring peace of mind.