The rule should only care about enclosing function/class scopes. For example if an ObservableScope is received as a parameter to a function and then simply used inside an 'if' block (technically a different scope), that's not a problem.
The rule of thumb to avoid resource leaks is that you should never call ObservableScope methods in a callback unless the ObservableScope is directly passed to or created inside that callback. I had a go at codifying this as a lint rule.
Timo K.