– we document become/unbecome to act upon a “behavior stack” (which Tomasz picks up)
– the documented examples do not use the second argument to context.become, which means discardOld = true
– in 2.0.x it mostly works in simple cases because the original behavior is never replaced
– in 2.1.x that behavior has been kind-of retained: unbecome on a stack which would end up empty will reinstate the original behavior