Strange bug in Pharo 50 pay attention

When I want to add an instance variable to a class


Model subclass: #WorkspaceRev
     instanceVariableNames: 'textModel bindings'
     classVariableNames: ''
     category: 'WorkspaceRevisited'

I get a message like


Syntax Error: Unmatched ' in
WorkspaceRev methodsFor: 'bindiUnmatched ' in string literal. ->

the code of the method looks like that

ph editingModeMorph lineNumbersDisplayMorph bla'
     classVariableNames: ''
     category: 'WorkspaceRevisited'