Mitchell,
Thanks for the response. I am working on a rather large project (heavy sencha mvc) and we are trying to measure the feasibility of using the 4.1 beta. There are a lot of fixes we need, but I guess we will have to wait for the GA.
I just did a text search for AbstractFit in the whole 4.1.0-beta-1 distribution. The only place I found it was in the docs (they come bundled with a copy of 4.0.7 so that's to be expected).
Could you do a search for the text AbstractFit in your code, see where it comes from?