PR rebased on Github breaks the hub sync functionality to cleanup local branches when PR branch is deleted (after rebase)

[prashantkalkar]

Command attempted:
hub sync

What happened:
When Github PR is rebased, instead of merged. hub sync can not cleanup local branches as they does not seems to be merged.
I understand that Git will not report them as merged (as post rebase the commit SHA will be different even when branch changes exists in the main branch). I am hoping that hub sync can figure this out that branch contents exists in main branch.

I am not every sure whether it can be said as a bug, but it does feels like a bug / broken behaviour while using the hub sync command for local brach cleanup functionality.

More info:
NA