It seems there is a problem with obsolete classes. SystemNavigation default obsoleteClasses -> an Array(AnObsoleteWordArray AnObsoletePath AnObsoleteLine) If you then browse WordArrayForSegment, you will see that it is a subclass from AnObsoleteWordArray. Changing that, back to WordArray, and then evaluating: Compiler recompileAll. Smalltalk fixObsoleteReferences. SystemNavigation default obsoleteClasses ->>> an Array(AnObsoleteWordArray) But I cannot get rid of that final obsoletClass. I tried inspecting SystemNavigation default obsoleteClasses and checking the pointers to the obsolete class, but I couldn't find anything. BTW, issue 3864 is failing because of that. cheers mariano