bootable disk doesn't appear in Startup Pref pane

iMac 2.66; 10.6.8

Iomega external 128gb SSD

I clone the iMac twice a week to the SSD so that I have a bootable backup. When I boot up off the iMac and open the Startup Disk pref pane, the SSD does not appear.

The SSD's icon DOES appear when I hold down the option key on startup and it boots fine. After booting up off the SSD, the SSD's icon DOES appear in the Startup Disk pane.

Also, I have another external disk, an SATA, that I cloned to and booted up off just to see if the SSD is recognized in the SATA's Startup Disk pane. It isn't.

Anyone know why this is happening and if it can be corrected?