The AbstractMathTransform.Inverse class is non-static. This cause the compiler to generate a this$0 private field. But this synthetic fields may not be the same across implementations of different Java compilers. Consequently reading a class serialized with an Apache SIS library compiled with a different compiler may not recognize the fields that are named differently (see http://developer.java.sun.com/developer/bugParade/bugs/4211550.html). We should use static inner class with a named field (e.g. "forward")instead. This is an incompatible change, but AbstractMathTransform.Inverse is protected rather than public.
In the particular case of AbstractMathTransform.Inverse, it also avoid a minor strangeness. Since we extends Inverse in different classes, we saw the synthetic this$0 field duplicated in each subclass. Using a named field instead will avoid that.