strange error(when hitting walltime limit)

[Glen Beane]

When I use mpirun, if a job hits its walltime limit I get a message
stating that.  With mpiexec if a job hits its walltime limit, I get a
mpiexec: warning: main: task x died with signal 15 in the stderr file. 
I know the job hit it's walltime, and prior to that it was running
properly.

I'm using the latest version of PBS Pro.  Is this normal behavior of
mpiexec?