There was a conflict with the voyage theme due to that theme also using bootstrap.
I have fixed the problem.
You can download the fix here:
This version is not on general release just yet. I would be really grateful if you would let me know as soon as you can whether the problem is now fixed so I can release it to everyone.
Also, with this version I have enabled internationalization. I noticed your site is in German. If you would be willing to translate the plugin messages into German that would be very helpful plus you will get to have the plugin in your own language! Let me know if you would like to do this and I'll let you know what you need to do.
I look forward to hearing from you.