Thanks for your advice. Unfortunately it did not help. I have Version 0.5.2+matrix.1 of INpuSTream Helper installed. What I tried was to delete existing CDM library and reinstall it what did not solve the problem. Then I tried to restore it but was only one backup given. After restoring it the playback issue was still there. Wtihin InputStream helper I could not find any other tweak to try out.
What else could I try?