Failed to Remove Scratch DMG

I've had some success running the base Instadmg.bash script on a 10.4.11 G5. I have run into an issue where my the scratch DMG won't unmount. I haven't edited the base script at all. Is this a normal operation? I don't see anything in the log other than 'Removing scratch DMG', and then if I look back in Terminal, I can see that the process completed but that the image failed to unmount. I'd be happy to provide any additional info.