This may not be the most common scenario, but where I work it is policy - daggy fixes are used whenever possible.
This means that we try to make fixes as close to the commit that introduced the bug. So I will routinely rebase a fix onto an old commit (before branches were made), then open 3 PRs for 3 maintenance release branches (target branches).
The issue here is that Jenkins reports that the fix commit was successfully built (or not), rather than reporting that the merge commit (fix -> target branch) was built. GitHub then marks all 3 PRs green/red, according to whichever job finished last, allowing bad PRs to be merged.