Please don't make buttons jump

jumping button

It’s a common occurrence that I’m trying to click the appearing Rebuild button on the top right (eg. after clicking Details on a github PR page, or using the Back button), and by the time I get there with the mouse, the whole area gets instantly redesigned and the button becomes longer, due to new text Rerun job with SSH, and worse, it gets fully shifted away, so I may click on the Open pull request Guitar Hero icon, Settings cogwheel or Follow project.

I think there should be a rule that says, don’t instantly reconfigure interactive affordances as it turns Fitts law on its head.