18. 4. 2020 v 22:25, Bruce Mutton <bruce@tomo.co.nz>:

I think it is a bug. If the user hides all of the centreline objects, and also hides all scrap objects (or something like that), then Therion should trap the error and exit in a controlled manner, rather than letting metapost get in a tangle and produce a mess of messages until it finally crashes.

Yes, it looks as it is bug. Because there are objects in that scrap - three stations from which Therion may „georeference“ sketch which is a part of the scrap too. Hide representation of objects means only to not include them in the final drawing.