Groups cannot be reused

In WriteableCommandLineImpl.java, the code after this comment:

// ensure that all parent options are also added

ends up rejecting what should be valid command-line args. If you make a group and use it as a child in more than one parent, which is a wholly reasonable usage of the API, I think the child only registers one parent and then the "int present" counting goes over its maximum and the args are rejected, because hasOption returns a false positive.