Here is a reduced test case: eval('"use strict"; undeclared = 1;'); This should throw an exception, and does without -m. But with -m it completes without throwing.

Summary of solution: - Change front end so it doesn't create properties for undefined variables in strict mode. - Change ic::SetProp to call stubs::SetName so it gets the full logic for setting a property, necessary to strict mode errors setting properties - Update stubs for JSOP_LAMBDA to match interpreter