Description of problem:
Once a system or user default of openmpi is set:

sudo mpi-selector --system --set openmpi-1.2.5-gcc-`uname -i` --yes

if MANPATH is unset by any other means, openmpi's mpivars.sh will set MANPATH
to, say,

/usr/lib/openmpi/1.2.5-gcc/share/man

Then, no other man pages can be searched.  (e.g., 'man ls' fails)

Suggested fix:
set MANPATH with trailing colon (:) if MANPATH is empty:

--- /usr/lib/openmpi/1.2.5-gcc/etc/mpivars.sh~  2008-05-25 01:28:57.000000000 -0400
+++ /usr/lib/openmpi/1.2.5-gcc/etc/mpivars.sh   2008-07-21 11:36:14.000000000 -0400
@@ -19,7 +19,7 @@
     if [ -n "$MANPATH" ]; then
        export MANPATH=/usr/lib/openmpi/1.2.5-gcc/share/man:$MANPATH
     else
-       export MANPATH=/usr/lib/openmpi/1.2.5-gcc/share/man
+       export MANPATH=/usr/lib/openmpi/1.2.5-gcc/share/man:
     fi
 fi
 

Note for this to take effect, after manual patching, must unregister and
re-register openmpi with mpi-selector so the scripts get re-copied to
/var/lib/mpi-selector/data/ (or just edit those target files directly)

The same applies to the *.csh scripts.

It's unfortunate 'man' won't find the man pages without setting MANPATH, but
from what I can tell (strace -e trace=file man mpicc  2>&1 | egrep openmpi), man
won't look in bin PATH elements "../share/man/".  Maybe a symlink to the man dir
/usr/lib/openmpi/1.2.5-gcc/man -> share/man.