the minimum and maximum constraints on a group do not take other groups into account

If you have a Group A as a child of Group B and you set a minimum or maximum on Group B, the presence or not of Group A will not affect GroupB. This is because Groups are never added to a CommandLine so .hasOption(A) returns false and so it isn't counted. WriteableCommandLine#addOption(Option) should be used to indicate that a Group is present if any of a Groups children is present.