I'm sorry if I'm adding on too late. I am having this issue also when using aspire with my Openbuilds 1515. I'm using a 1/8 Downcut bit. Did this ever get solved?
See Tramming: A generic guideline - tramming is usually the cause for lines in pocket cuts, due to tilting
Thank you for the link. I believe what is happening is something else though. It looks very similar to the picture in the first part of this thread. Sections of the pocket have no problems but it seems the parts that are close to the edge cut deeper. It's almost as if the machine is settling as it continues along the toolpath.
Here is a picture. If you look at the one toolpath near the center. it's deeper than the rest on both sides. This makes for a very uneven bottom surface of the pocket. I am using a downcut bit but sometimes the height difference is significant.