Why does xlog.c not treat COMMIT_PREPARED/ABORT_PREPARED as commit/abort?

There's a bunch of code in xlog.c that special-cases commit/abort records
for purposes of controlling replay, ie whether you can pause before/after
a particular xlog record, extract a timestamp from it, etc.  This code
does not, and apparently never has, counted COMMIT_PREPARED or
ABORT_PREPARED as commit/abort records.  Is there a good reason for that,
or is it just an oversight?

I noticed this in investigation of bug #11032, which is a side effect
of the fact that xlog.c doesn't believe there's any timestamp to be
found in COMMIT_PREPARED records.  But more generally, they can't be
used as recovery targets, and I don't see a reason for that.

Assuming we agree that this is a bug, is it something to back-patch,
or do we not want to change back-branch behavior here?
        regards, tom lane