Cutting the line art of a symbol?

I need to select part of the Line Art of a layer. To this end, I use the Line-Art module to select the line art, use this as input of a Cutter module (I could have reversed these steps, but it seems to be irrelevant). This works.

However, this does not seem to work for a symbol: the Cutter makes it impossible to select the Line Art. Whenever I add the Cutter, the final result also show the colour art; disabling the Cutter brings it back.

Any help is appreciated…

This was confirmed as a bug by Toon Boom support.