Are you using P5? I do and find that canceling when rendering in the same window is not a problem. However, canceling a render in a new window will result in a "hang". I guess the newest update is suppose to help with some of that, but I never installed it as I pretty much know how to maneuver around the few nuances that P5 has since I updated with the 2.1 or 2.2 updates. I don't have the time to learn new nuances right now :)