follow-up: removing the breadcrumbs does not completely stop the status bar from resizing split windows. The split window width still changes by a few characters depending on the line/column numbers, and on whether there is a "selected character" count.
To be blunt, this is absurd. Why do the split window resize at all? I adjusted the split to the position I wanted. It should not change.
I do still believe this is a status bar issue. The change from version 9 is that each split view has its own status bar, instead of there being only one status bar which is shared (shows details for the active split window). I can see why someone figured that might be confusing, but honestly, it was much, much better than this.
Anyone have suggestions for anything I might try? Removing the status bar would be a last resort, since I do make use of the line/column numbers at times.