bug#22330: eshell/grep/next-error problem

[bewaremyethnicheart]

There seems to be a problem with multiple greps and the next-error feature 
within eshell.  To reproduce bug:

1. Open emacs (23.1.1 or 25.1 both exhibit behavior, so assume other versions 
likely do as well). 
2. M-x eshell
3. From within eshell:
       grep string1 file
4. M-x next-error (this should work)
5. M-x eshell (or switch to existing eshell buffer)

6. From within ehsell:
       grep string2 file 
7. M-x next-error (this fails with "Moved past last grep hit" message in 
minibuffer, even though there are valid grep hits on second grep).

Killing the grep buffer, the eshell buffer, reloading the file all result in 
the same behavior upon further greps--"Moved past last grep hit".  Only 
quitting emacs and restarting it gives proper behavior --for the first grep 
only.

Thanks!

Joe