As far as I can tell after speaking with 2 different Fox Service technicians, nobody seems to know why their forks have this well-known problem with negative air pressure increasing and migrating, and not re-equalizing.
I don't understand the whole thing, but there's only one port that allows air to move from the positive to negative chambers. I've now had 2 of the 2015 RC2's and both began doing the same thing after about 3 months of riding: the stanchions started not fully retracting when I am standing next to bike, compressing fork as far as possible and immediately lifting front tire off the ground. I tried "burping" with a ziptie between dust wipe and stanchion, but nothing there. I will next try removing the top cap and rod and slick honey it as directed and see if that fixes the problem, as well as do an oil change.
One year ago, with my first 2015 RC2 (160/36 - 26") Fox had me send it in under warranty - they ended up sending me a brand new fork, but it was never clear what the problem was. I hope I don't have to send this one in. Even one of the techs I talked to said he had asked an engineer about this who also didn't know what causes this problem(!) Hard to believe as it's a well-known issue, and I'd like to know how to prevent it. Btw, I have not been riding at high altitudes. I have bottomed out a few times - but why should that, if it has something to do with this, be the cause?? thanks!