Scroll for page shifts making it hard for user to locate page while switching between code and page

In all honesty I found this very difficult to reproduce in any kind of consistent way. Following the steps in the video lead to the issue being exhibited maybe 10% of the time.

With my fix (which is a bit of a stab in the dark) I've not been able to reproduce the issue - but I'm not confident I've identified the reason the issue is occuring so maybe it just makes it better but there is still some underlying race condition that could still happen.

I could only reproduce the symptoms as reported once, but I approved the code as it does address the possible cancelling of a callback we didn't actually want cancelled. However, because the issue is difficult for me (and @jessebaker) to consistently reproduce, I think it would be best if @neha_bawankar (the reporter) tried this out before this gets merged. That's just to ensure we don't need to re-open this - it doesn't appear to be the sort of change that would introduce a problem.

I have merged, this can be tested on 0.x now @neha_bawankar