I'm unsure of where Grub's official upstream repository is located but I was able to locate the following: http://savannah.gnu.org/bugs/?18224
Perhaps it would be prudent to submit a bug upstream (if it has not already been done) to explore the possibilities of making a small change to ensure USB devices do not halt the boot process.
I agree that it would be best to eliminate the possibility of a BIOS issue first. Most USB boot device issues I have been quickly resolved by updating the BIOS. A quick google search lead me to this site: http:// support. asus.com/ download/ download_ item.aspx? product= 1&model= P4S800D- X
Can you please verify that the following:
1) That you have the most current BIOS revision installed.
2) That you are not using a USB hub to connect your keyboard to your PC
If the previous suggestions don't resolve the issue then this bug may be related to: https:/ /bugs.launchpad .net/ubuntu/ +source/ gfxboot/ +bug/35530
I'm unsure of where Grub's official upstream repository is located but I was able to locate the following: http:// savannah. gnu.org/ bugs/?18224
Perhaps it would be prudent to submit a bug upstream (if it has not already been done) to explore the possibilities of making a small change to ensure USB devices do not halt the boot process.