It seems the developers of the CAQDAS software suite MAXqda have made a few innovations. Now, in addition to a sophisticated code-and-retrieve memo system, users are able to integrate those codes into MAX Maps, which is something of a cross between traditional mindmapping and Boolean graphical concept mapping.
It's not cheap ($445 for a singel academic license) but MAXqda is one of the most established names in CAQDAS software - meaning that not only is it generally more sophisticated than some latecomers, but that it likely has fewer bugs.
There's a 30-day free trial, should you want to check it out (or perhaps include it in a research methods course?).