Using appsaudit or using the command line tce-audit tce-remove works as expected with no errors when used as designed.
Please read Tiny Core v3.5 release announcement. There you will see:
* Updated appsaudit to support removing ondemand uninstalled extensions without rebooting.
The key word is uninstalled.
I ran your specific case of tucan and all worked as described and documented when tucan appeared in both wbar and ondemand menu but I had not installed it.
Once an ondemand extension is loaded into the system, i.e., creating all the symlinks and made available for use, then it behaves the same as any onboot extension. The removal will be done upon shutdown to ensure the integrity of the system.
I can only surmise that you had tucan installed/