This should be so since 0.9z-7. Well, sort of because it is a bit wacky. Or I don't know anymore how (when) it exactly should work that XXHighEnd automatically starts and when not. There was a sort of "design" topic about this back at the time.
Anyway I know this doesn't show consistent behavior.
I think it should never do (start) when using Alt-s.
I think it should always start at normal end of playback.
I think it just won't do that when "End at track" (or Alt-k) is being applied.
And it also is related to Phase Alignment and therefore buffer size.
Peter