Not a real bug, maybe future feature.
Running sce-ondemand non-existing_extension creates an /tce/ondemand script for the item even though it doesn't exist. Simple typo in package name can leave user wondering why item added to ondemand doesn't work. Since sce-ondemand -l (list of available SCE(s) to add to ondemand) functionality already exists, query possible to check the entered extension name against the sce-ondemand -l output and report error if the extension isn't available to add to ondemand.