When I try

(MCWorkingCopy forPackage: (MCPackage named: 'NautilusRefactoring')) unload

NautilusUI allInstances do: [ :inst | 
SystemAnnouncer uniqueInstance unsubscribe: inst].
Smalltalk garbageCollect.

(MCWorkingCopy forPackage: (MCPackage named: 'NautilusCommon')) unload.
(MCWorkingCopy forPackage: (MCPackage named: 'Nautilus')) unload 

I get the attached system. I do not understand why SpecDebugger has something to do with navigationHistory.

Any idea?
I also think that we are not good at making sure what we load can be cleanly unloaded. Without that discipline we will never have 
a modular system.

Stef