I noticed it several times before Ulillillia, It seems to be caused by the shadows being listed as no longer visible, some kind of origin of the shadow or similiar.

I've had a good scan through the manual and couldn't find anything about it, other than turning stencil on/off.

Maybe I should raise it in the Ask Conitec thread....

Edit: Thanks for replying, at least I know I am not loosing my marbles here