I was watching the webinar this morning and Pam Heller is adamant that all the dies are set for a full 1/4 inch seam. It you do not cut on the straight of grain, it can cause your fabric to stretch and it snaps back when cut. Also, if you use a mat too big for the die or even what you are cutting can cause a bad cut because the larger mat can move the fabric. The only time you don't use the straight of grain is with the strip dies.
I had problems cutting my hexagons until I started watching their videos.
If you are on Facebook they have some great videos. Every Wednesday at noon Central time they broadcast live on Facebook wth a new thing.
Just FYI - I do not work for Accuquilt or have any vested interest. I am just a huge fan.