Private field inaccessible in closure when using a subclass

If a class defines a private field and a method that uses a closures referencing this private field, then a groovy.lang.MissingPropertyException is thrown any time this method is called from a subclass.

It can be reproduced in the groovy console with the script in attachment. If "iterate" is called on the parent it works (text is appended to stdout - no exception), but if it is called from the subclass it fails (only the text from outside the closure is displayed and then an exception is thrown).

This issue come from a deeper investigation on http://groovy.329449.n5.nabble.com/Exception-when-extending-ASTTransformationCustomizer-td5630073.html