if grep is handed an pipe on standard in, it is not correctly checking if it's a directory before acting on the '-d recurse' option. 

from grep man page:

-d ACTION, --directories=ACTION
              If an input file is a directory, use ACTION to process it.  By default, ACTION is read, i.e., read directories just as if they were ordinary files.  If ACTION is skip, silently skip directories.  If ACTION is  recurse, 
read all files under each directory, recursively, following symbolic links only if they are on the command line.  This is equivalent to the -r option.

behavior in Fedora 21:

ahecox@localhost ~ $ which grep
/bin/grep

ahecox@localhost ~ $ grep -V
grep (GNU grep) 2.21
Copyright (C) 2014 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Mike Haertel and others, see <http://git.sv.gnu.org/cgit/grep.git/tree/AUTHORS>.

ahecox@localhost ~ $ file foo
foo: cannot open `foo' (No such file or directory)

ahecox@localhost ~ $ echo foo | grep foo
foo

ahecox@localhost ~ $ echo foo | grep -d recurse foo
rpm-qa:foomatic-db-ppds-4.0-44.20140707.fc21.noarch
rpm-qa:foomatic-4.0.11-6.fc21.x86_64
rpm-qa:foomatic-db-filesystem-4.0-44.20140707.fc21.noarch
rpm-qa:foomatic-db-4.0-44.20140707.fc21.noarch
.svn/pristine/89/893e400d588348f701bcbaf75e4a15903c40d4db.svn-base:#usage() { pusage: "foo"; }
... (many, many lines clipped, recursing starting in the CWD)

previous versions behaved inline with the description of the man page (checking that the input is a directory before following the action). The latest test box I have is RHEL 6 (grep version 2.6.3) so not sure that this is a recent change.

Let me know if I can help test or answer questions.