Hello Malte
It could be possible that your code is somehow unusual and JRebel has problems with it as the use case is not in our test suite.
Can you send jrebel.log to support@zeroturnaround.com along with code/configuration snippets of how your are configuring and using the genreConverter ?
Guide for generating jrebel.log can be found from http://zeroturnaround.com/software/jrebel/learn/sending-log/