If you clone from a hda to a hdb that means you read from a master and write on a slave. The two disks are on the same ribbon cable.
By removing the original disk, which is a master, and put the target in to work alone that disk must be reset as the master in order to boot as the original.
hda=master of the primary IDE channel
hdb=slave of the primary IDE channel.
An IDE disk has jumper at the back to configure it as a master, a slave or cable select. If you set it on cable select then removing its middle connection and plugging the disk to the end connector automatically makes it a master.