PokerTracker

I just tried out a tourney at 888 poker, and PT4 wants me to believe I am playing at 10handed tables, but it was 9-handed. Does this have to do with "Treat as" option that I disabled because of slow import when I did initial HH import?

Treat As does not affect 9 or 10 seat tables, and unfortunately there is no way to tell whether an 888 full ring table has 9 or 10 seats, as their hand histories do not specify this and they have both.
The development team are aware of this issue and we're discussing ways to work around it, but we're also in contact with 888 (and other sites) to try to persuade them to add this information to the hand history files so that we can deal with this automatically.