Hi @amaurer,
Welcome to the community 
If you are still in the development phase of your project, you may want to look at the improvements in GSNv2 which is in development at OpenGSN.
I assume that this only impacts your testing as assume that you will only be deploying your contract once. Let me know and I can try reproducing.
GSN Provider and GSN Helpers are in maintenance mode. We are no longer actively developing new features for these projects, and will only be releasing fixes for high severity issues until July 2020. Read here for more info.