bug#23906: 25.0.95; Undo boundary after process output is not consistent

[Eli Zaretskii]

> From: Markus Triska <triska@metalevel.at>
> Date: Wed, 06 Jul 2016 19:56:30 +0200
> 
> 7) Now the point: *Most* of the time, after undo, the buffer is exactly
>    as it was before. But sometimes, about 1 out of 7 times, after undo
>    is pressed, the characters "%@ " remain at the end of the buffer:
> 
>    %?- time(ceiled_square_root(2^10000, R)).
>    %@ 
> 
>    These three characters ("%@ ") are inserted by ediprolog before
>    receiving process output, and in most cases removed after the undo.
> 
> The issue in this case is not so much that the %@ appears in the buffer,
> but that it is not handled consistently. Most often (and preferably), a
> single undo removes both the process output _and_ the %@, but sometimes
> a single undo removes *only* the process output, and the %@ remains. The
> behaviour I desire is that C-/ consistently removes everything that was
> inserted in direct sequence, both the "%@ " _and_ the process output.

Given the fact that (AFAIU) undo for subprocesses is caught by code
that runs off a timer, isn't the above expected?  Phillip?