I've run into this a couple of times after installation of Linux on a new system.
I'm guessing this has to do with a failure to write a new boot loader on the system? I've seen it on both Redhat and Slackware installs, and on different systems.
A zeroing of the hard drive (wipe) seems to clear it up, but then I have to go through the Linux reinstall.
Is there a faster way to fix it?