Take PharoCore-1.0-10470-BETA.1 Select the 1st item in the left pane (Delay class) Select 2nd item in 2nd pane ([] in Delay class) Yields: Message not understood: receiver of "keywords" is nil Same occurs when clicking on other items. Seems to be some hacky code in CompiledMethod>>#getSourceFor:in: (See comment in final return expression.) [This does not seem to be related to issue 751.] - on