grep outputs "input file is also the output" when running update-grub

[Dan Kegel]

On ubuntu 12.04 alpha1, fully updated, running update-grub outputs
grep: input file `/boot/grub/grub.cfg.new' is also the output

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=651617 says two contradictory things about this:
1) that the smallest test case for this is
   sh -c 'echo foo >bar; exec >>bar; grep -q foo bar && echo found >&2'
2) that the smallest test case for this is
  grep -qr . > out

I can verify that #1 is correct, and #2 is incorrect, i.e. on the system where grub-update outputs the error message in question, only the first one fails:

dank@a3850:/tmp$ sh -c 'echo foo >bar; exec >>bar; grep -q foo bar && echo found >&2'
grep: input file `bar' is also the output

dank@a3850:/tmp$ grep -qr . > out
^C

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.