Unchecking 'read underlay art' ignored for symbols?

I like to start my animation with a rough sketch in the Underlay drawing layer, which is subsequently refined in the Line art layer. I usually keep my rough underlay sketch, and switch it off in the Network view Drawing Layer properties. Works like a charm. However, when I store drawings in the Library, for instance when building puppets, this doesn’t seem to work, as unchecking ‘Read underlay’ seems to be ignored for symbols. Am I overlooking something, or is this a bug?