Hi guys. So we have a case where we can reproduce the problem. See http://code.google.com/p/pharo/issues/detail?id=6644
If you take a Pharo 20274 and load this slice: SLICE-Issue-6635-Removing-class-does-not-remove-class-tag-CamilloBruni.1 , the �#testInstanceSideMethodsWithNilKeyInLastLiteral starts to fail and we have lots of instance side methods with nil in the last literal (in fact, from the package that the slide installs).