Windows – cygwin grep running 680 times faster via ssh than via remote desktop

Running grep by opening Cygwin terminal via Microsoft Remote Desktop to Windows Server 1012 R2(same as natively?):

Administrator@MYSERV /cygdrive/d/bin/beta
$ time grep -inowf matchfile_431184247462809.temp infile_431184247462809.temp > delme

real    1m40.568s
user    1m40.405s
sys     0m0.140s

Exact same command, on same files, executed when connected via Cygwin SSH:

Administrator@MYSERV /cygdrive/d/bin/beta
$ time grep -inowf matchfile_431184247462809.temp infile_431184247462809.temp > delmessh

real    0m0.148s
user    0m0.140s
sys     0m0.000s

grep.exe executable is the same, the output file is the same, but the run time is split second vs. almost 2 minutes.

Given that cygwin SSH runs under special user setup, i tried to ssh localhost on remote desktop; the runtime: 1 minute and 40 seconds.

Is there some logical or illogical explanation for this? Any settings that I can check on Windows Server 2012 that artificially suppress remote desktop processes?

Update:
running C:\cygwin\bin\grep.exe from Windows command line cmd also is instant. So there is an issue with Cygwin terminal.

Update 2:
I googled that having dead file shares in PATH can slow Bash terminal down. Contrary to my initial hope erasing $PATH variable did not do anything. I also do not have any dead links in PATH.

Solution, kudos to @Paul Haldane:
Grep seems to be thrown off by $LANG value of en_US.UTF-8, which is default in Cygwin. This hits regex performance especially hard. Running grep -F was also slower but only by a factor of 4.

Here is a verification on a separate server:

$ echo $LANG
en_US.UTF-8

$ time grep -inowf matchfile_431184247462809.temp infile_431184247462809.temp > delme

real    1m56.425s
user    1m56.218s
sys     0m0.171s

$ LANG=''

$ time grep -inowf matchfile_431184247462809.temp infile_431184247462809.temp > delme2

real    0m0.286s
user    0m0.265s
sys     0m0.015s

$ diff delme delme2
** no difference **