Sorry I posted it befor in the wrong place.
This Bug appears if the analyse file function is called. The material is .flac created by EAC with Vorbis tags and cover included.The joined result is fine anyway.
The Version of the Audio Joiner is 1.9.0 (Build 331).
Windows Version is 8.1
I moved this again since it does not relate to Helium itself, sorry for the confusion.
The joiner is an product we no loner maintain since it was build on our old Helium platform.
The good news is that we are working with an improved version which will be integrated into Helium 12.