/etc/profile has the line:

PATH="$PATH:/usr/X11R6/bin"

which unconditionally changes the path.  This is correct behavior if bash
is spawned directly by /bin/login, but in other situations it can put
/usr/X11R6/bin into the path twice. 

This happens is with an ssh login, since ssh doesn't use /bin/login unless
the UseLogin option is selected.  Another way to reproduce the problem is
to use 'su - foo' to change to the user foo.  The best fix, imho, is to
have /etc/profile do a check before modifying the path.  Here is one of
many ways this can be done (not the shortest way, but at least its not too
cryptic):

echo $PATH | /bin/grep --silent /usr/X11R6/bin
if [ $? -ne 0 ]; then
  PATH="$PATH:/usr/X11R6/bin"
fi