Every time the frequency changes on the CPU, the plugin changes it's size. When used with fast update intervals, this makes the entire panel flap back and forth. It would be good if the size was constant, at the maximum CPU frequency (or the largest size needed so far). I could not find any options to affect this behavior.
This should be fixed in 1.1.1 actually. Are you sure your version is up-to-date?
No, you are right. The version in Debian Jessie (stable) is 1.1.0. I did query before I filed the bug, saw nothing and figured it was a new problem. I must have searched badly, I apologize. I marked it as resolved-duplicate/10385.
*** This bug has been marked as a duplicate of bug 10385 ***