For the sake of curiosity, I gave a try to: http://code.google.com/p/pharo/issues/detail?id=331 Instead of breaking the image, or tracking the senders of = (not my cup of tea), I simply instrumented my image with a Notification, and caught it with a MessageTally. This showed that String = Symbol is used in the #intern: / #lookup: process These are the method that check if such a Symbol equal to that String already exist or not, so as to guarantee uniqueness of Symbol. This is the first equality to be cleaned up before making any other change in the image. Beware, implementation of such core method should care of speed ! (See issue 331) If anyone one else wanna report other String=Symbol use case, welcome, the instrumentation is available in 331. Nicolas