Why is my pumpkin pie filling separating from my cake mix?
I wonder if this has something to do with the density of the cake vs the pie filling. This may be a similar phenomenon as when chocolate chips or nuts sink to the bottom of a brownie during cooking. 

I am not entirely sure how to solve this but one thing to try would be to mix the pie filling with the wet ingredients for the spice cake mix and then mix it all together. My hypothesis is that the pie filling isn't incorporated into the cake mix well enough (even though it may look well incorporated) and mixing it with the wet ingredients thoroughly may allow the eggs (i'm assuming eggs were involved) to set the mixture as a whole more evenly.