Mumble's GitHub issues use the same priority scheme as Qt (as of Feburary 2017).
|priority/P0 - Blocker||MUST be fixed ASAP. Issues that prevent further development; legal issues; serious data loss issues; build issues for platforms we provide binaries for.|
|priority/P1 - Critical||Urgent and Important, will STOP the release; Regressions from the last version that are not edge cases; Data loss; FTBFS for platforms we don't provide binaries for; All but the most unlikely crashes/lockups/hanging; Serious usability issues and embarrassing bugs; Bugs critical to a deliverable|
|priority/P2 - Important||Not Urgent, should be fixed, but will not stop the release.|
|priority/P3 - Somewhat important||Can be fixed, but doesn't affect the release in any way.|
|priority/P4 - Low||Would be nice to fix, but it's not very important.|
|priority/P5 - Not important||Not relevant and not urgent.|