Thanks for pointing this out Daniel.  I can recreate this issue with the log files you provided earlier.

I think the problem here is that you are combining log files which do not share the same schema. This use case is niche as most customers who merge files are merging the same schema.  So, I think it is a symptom of some of the other issues you have raised.  Now is a good time for us to reconsider how we work with schemas like this. 

I will look at this issue as we are debugging some of the other issues you have raised.  I will post back here when I have something.  At a minimum, the tool bar buttons should not behave like that - it's very user unfriendly.

Hi,
I forgot to mention: 
Have you noticed, that Reports don't work on Merge nodes?

You can only enable "Show Dashboards", but this won't do anything other than open the single "Log Data View" tab. All other buttons just do nothing at all.

Hope this helps!
Best regards,
Daniel