This bug is internally related to same implementation issue in ACG as identified in
GROOVY-3156. Even this is case of a method call expression explicitly qualified by "this" being made inside a closure when compileStack contains a variable of the same name as the method.
The patches supplied with
GROOVY-3156 fix this issue as well on versions 1.5.8, 1.6-RC-1, 1.7-beta-1. I have test verified.