I'm not sure if I'm missing something, but there seems some strange behavior that I don't understand. The value of a block variable changes when stepping over a method that acts on that variable. I encountered this in Spec, but that seems co-incidental to the behaviour. SETUP 1. The attached "My-Spec-Tutorial-BenComan.1.mcz" (i.e. Bahman's tutorial) was loaded into build #30564. 2. A breakpoint was inserted after the first "e generateArguments" in... SpecRowLayout>>privateAsArray | result shouldCheckSplitters | result := OrderedCollection new. shouldCheckSplitters := false. (self commands reject: [:e | e isSplitter ]) do: [:e | ...lots..hidden.for..conciseness.... e generateArguments. self haltOnce. "<------------------" e asSpecElements do: [:el | result add: el ]]. 3. The following was evaluated... Halt enableHaltOnce. MyFirstWindow new openWithSpec: #defaultSpec. OBSERVATION 1. When the debugger opened at the breakpoint e = a SpecLayoutAdd 2. But after stepping over #asSpecElements e = an OrderedCollection() So how did the value of 'e' change? Where... SpecLayoutAdd(SpecLayoutSend)>>asSpecElements ^ {self selector.}, self arguments SpecLayoutAdd(SpecLayoutSend)>>selector ^ selector SpecLayoutAdd(SpecLayoutSend)>>arguments ^ arguments This was on Windows 7. Since files.pharo.org is offline, I wasn't able to try a newer VM. My current was... NBCoInterpreter NativeBoost-CogPlugin-EstebanLorenzano.18 uuid: a53445f9-c0c0-4015-97a3-be7db8d9ed6b Mar 13 2013 NBCogit NativeBoost-CogPlugin-EstebanLorenzano.18 uuid: a53445f9-c0c0-4015-97a3-be7db8d9ed6b Mar 13 2013 git://gitorious.org/cogvm/blessed.git Commit: 412abef33cbed05cf1d75329e451d71c0c6aa5a7 Date: 2013-03-13 17:48:50 +0100 By: Esteban Lorenzano <estebanlm@gmail.com> Jenkins build #14535 Win32 built on Mar 13 2013 18:49:42 Compiler: 4.6.2 VMMaker versionString git://gitorious.org/cogvm/blessed.git Commit: 412abef33cbed05cf1d75329e451d71c0c6aa5a7 Date: 2013-03-13 17:48:50 +0100 By: Esteban Lorenzano <estebanlm@gmail.com> Jenkins build #14535 NBCoInterpreter NativeBoost-CogPlugin-EstebanLorenzano.18 uuid: a53445f9-c0c0-4015-97a3-be7db8d9ed6b Mar 13 2013 NBCogit NativeBoost-CogPlugin-EstebanLorenzano.18 uuid: a53445f9-c0c0-4015-97a3-be7db8d9ed6b Mar 13 2013 cheers -ben