Hello, Last week I had a error due to a strange behaviour: I had an instance variable and an accessor to this instance variable. The instance variable is instanciated at the initialization of the class. When the error occure, the instance variable is not nil (when inspecting it from the debugger ). But, when evaluating the accessor, it return nil. This occure in the pharo 1.0 dev image. I test it this morning on a clean image and on a click image with moose. It seems that the bug is specific to moose. If you want to reproduce it: Download the last version of Merlin from www.squeaksource.com/DelaunayTmpStuffs. run the method MerlinExamples class >> parametrizedMorphDropLists. it should work correctly. Now restart, load moose (load ConfigurationOfMoose, and evaluate 'ConfigurationOfMoose loadDefault') and then load Merlin from 'DelaunayTmpStuffs'. It should raise an error and you should be able to see this strange behaviour. From the debugger, evaluate 'self dropList' in MorphDropListPart. After showing this bug to Marcus, it seems that something is not weel compiled at one point: browse the method 'dropList' in dropListPart. Now, click on 'view' and 'byte code'. The offset indicated is 10 whereas it should be 15