This wasn't necessary before, because the only available branch sorting option
was by recency, so the sort order couldn't change except by checking out
branches. Now, you can sort by committer date, so the branch order can change by
fetching; in this case it's important to keep the same branch selected. One
important use case is to rebase the checked-out branch onto master; you select
master, press "f" to fetch it (this can now change its position in the list),
and then press "r" to rebase. To make this work smoothly it's important to keep
master selected after pressing "f".
