Have a look in your Graph Editor to see if you can spot the change in values on your fur length. I've not worked with Fur before, but if you can key it, it should be visible in the graph editor when you select it.
I do almost all my animation tweaks and changes in the Graph Editor. If I had two screens I'd keep my Graph Ed and Hypergraph windows open on the second screen!
-Jacques
Poly-pushing on a '96 SGI O2