A few minutes ago I found a kawl in the pumpkin patch, but I haven't got the achievement:

Kawl Finder Find the newest special minion in the Pumpkin Patch! (Kawl)

0/1

I was so happy that I forgot to make a screenshot:(

I think you have to find it on the year the Kawl was the special minion to get the achievement... so that one is retired I believe.

But there is no date to find it like the slivyne achievement:

Slivyne Catcher Catch the Slivyne from the Pumpkin Patch in 2011!

It has no date but like the Oowel achievement it is only active the year that it is the newest. So this isn't a bug. Believe me...I wish I could get the Oowel achievement since that is the only old one I don't have.