Error messages stopped occuring a few days after my last update to this post.
Together with Veritas we verified that EV tried to roll back these items.
The initial cause of the problem is still a bit unclear.
Further analyzing the eventlogs showed us that EV reached the storage queue threshold a few days before these errors occured and refused to accept new items. At this time the customer set the shortcuttimeout to 0 as he wanted to reset the pending items. Not sure but the rollback of EV may be related to this.
If it is occuring again i'll try to analyze this and update the post.