Classloading problem for getting a resource

We are using Betwixt and some of our unit tests fail when run using
surefire, but run fine in IntelliJ or Maven 1. Betwixt looks for
descriptors with the name of the class + .betwixt to control how
something is written out in XML. It uses the construct:
myClass.getResource() to find the .betwixt file.

E.g. com.mycomp.MyClass -> com/mycomp/MyClass.betwixt

We have a betwixt file for the java.util.Date class. However, betwixt
seems to be unable to pick it up when using surefire. I have created a
small test that shows the problem and have attached it.

I tried with version 2.2 using different configurations (never, once, pertest) and with version 2.1.3 (default configuration)