Inactivated users re-aliased to “Unknown user #####“ changes last activity date on already merged PRs

When a user is inactivated they are eventually re-aliased to “Unknown user #####“.

All PR’s that they merged (perhaps had any activity in) suddenly have their last activity date updated (in PR list view). Actually inspecting the PR still shows the “proper“ last activity (if PR was merged 2 weeks ago, most recent entry in PR’s activity tab is the merge event from 2 weeks ago).

But in the list of PRs view (e.g. https://bitbucket.org/…/pull-requests/?state=MERGED) things merged weeks ago suddenly have last activity dates of today (presumably the time the user was re-alised to “Unknown user #####“). This erroneously changes the ordering in the list view, without an actual activity logged to indicate why.