Actually it's the same error repeated 4 times as Is Message View is reused (via its parents) multiple time.
Since all this occurs in the Dummy pane, you can simply ignore it, as this pane is not included in the runtime display.
These errors are a result of unchecking the Faster validation option in Window -> Preferences -> Tersus -> Validation
I've uploaded an updated version to http://www.tersus.com/#Id=139 that fixes this "esthetic" issue.
For best results, use the Firefox browser..