I have been keeping track of how many pumpkins that have moved through my inventory and while I have found 115 so far, only 70 have been tracked for this achievement? I have tried waiting a bit after I click on a pumpkin before moving on to see if the problem was that I was moving on to fast, but that does not seem to make a difference.

[edit]The problem persists as I have found about 370 pumpkins, but only 205 have been tracked for the achievement.

I want to say that I am experiencing this problem as well. I am finding more pumpkins than the achievement says, which is frustrating because I only need literally two more to reach 1,000 of them, and I've definitely found those two, they just haven't been counted. :(