The goal would be to track the status of an issue (somewhat) independently for different branches.
When creating a bug task, you specify the branches that are relevant, and in each branch it would come up as open.
That way, one can check if a problem is fixed in all relevant branches. This would require interpreting branching and merging along with the task <-> commit relation, I would imagine.
After Releeph, we may have some tools for tracking where changes have merged, but do not plan to bring this to tasks anytime soon.
This is difficult to do automatically in the general case in a way that aligns with user expectation. For example, suppose you push a new branch which is one commit ahead of master. The new branch technically has fixes for thousands of tasks in it. If we go update all those tasks it's super confusing; if we don't it's potentially equally confusing. I think we actually have to track explicit merges; Releeph will give us tools to do that.
So this may get supported in some way, sort of, eventually, but it's so far off that the path between here and there isn't even clear yet.
You could try using a custom field in the meantime, although you'd have to update it manually.