Ok, I'll try to record the issue. The problem seems to be with the sound in some way. SEM doesn't really kill Spark for good (and vise versa). The other instrument just becomes mute. Buttons work, lights light. The GUI seems to work on both of them. Just no sound output from the other one (the one that has been launched first). And as I told, everything works fine as plugins in e.g. Ableton.
/Ari