For bugs with milestone "Latest_Git" which branch should be used to test it, Master branch or the latest QA branch (like QA_4_1 currently)?

I am asking this because I have seen few bug tickets (Latest_Git, open tickets) which seems valid bugs if tested (reproduced) using Master branch but not if tested using QA_4_1 branch.

Is master branch only for receiving feature requests?
Why are bug fixes not applied to master branch?