Kevin, Its one of those things I notice being a carpenter. My deck is PT (12yrs old)
Even nowadays I could brush the sap with my finger and still get alot of powdery residue.
Deck has been sealed numerous times and it still comes out.
PT lumber is normally Southern yellow pine, which is known for a certain resistance to rot and insects, but it also has a lot of sap which takes many years to dry out.
Add the whole PT process and you can see what I mean.
Tim