In order to substitute "where you boot from" for UUID=0, you first must know where to boot from. The way the boot loader decides where to boot from is by searching for the correct UUID. If the UUID has changed, or duplicated, then it can't figure out where to boot from, so it can't figure out what should be substituted for UUID=0.
In order to substitute "where you boot from" for UUID=0, you first must know where to boot from. The way the boot loader decides where to boot from is by searching for the correct UUID. If the UUID has changed, or duplicated, then it can't figure out where to boot from, so it can't figure out what should be substituted for UUID=0.