+ ----- Method: Behavior>>basicAddTraitSelector:withMethod: (in category 'traits') ----- + basicAddTraitSelector: aSymbol withMethod: aCompiledMethod + "Add aMethod with selector aSymbol to my + methodDict. aMethod must not be defined locally. + Note that I am overridden by ClassDescription + to do a recompilation of the method if it has supersends." + + self assert: [(self includesLocalSelector: aSymbol) not]. + self ensureLocalSelectors. + self basicAddSelector: aSymbol withMethod: aCompiledMethod.!

this should be fixed. A method which comes from trait should be always copied before installing into behavior. Otherwise, super sends won't work properly, as well as you may end up with a mess, where trait holding a reference to the non-existing behavior (added then removed) , because installing a method into method dict always changes its methodClass.