Moving pg_xlog to another drive

I'm trying to move my WAL to another drive, but am having difficulties
with this seemingly simple process. Every time I start up with pg_xlog
symlinked to my other drive, I get this:

FATAL:  could not open file "pg_xlog/00000001.history": Permission denied

If I move pg_xlog back into its normal place then things work fine. The
postgres user can certainly create files when using the symlink, so I
really don't think it's a permission issue... but I'm at a loss as to what
else it might be.

This is on CentOS 5 with the latest RPMs. SELinux is not enforcing (nor
logging any events when I do this stuff).