Hi Luc,
I'm going to do some research on my end, but would you be able to get the following information for us:
1. How long are you waiting to see if the job actually cancels? Have you given it 30 seconds, 10 minutes, etc..)?
2. When this occurs, what are you actually backing up?
3. What device are you using when this occurs? If you are using a tape drive, can you try the same test with a backup to disk folder and see if the same thing occurs?
4. If you are using the Advanced Open File Options (AOFO), try running a backup without that and perform the same test by canceling.
5. When this occurs, open up Windows Task Manager and see what process is actually pegging the computer out at 100% and let us know what that is.
Thanks.