Q: What is the blue line that links a node to the handle of a neighboring node?

Question: What is this blue line that joins a node to a handle?
I’ve encountered this from time to time – just a rendering bug I suppose?

Yes, that happens. Not necessarily blue, but your system selection color. Rearranging the node order fixes it usually. I think it has something to do with the closepath instruction, but I’m not sure.

This is a small bug with the selection drawing if the first node is a off curve point. I left it as an indicator.

So if I understand correctly: I suppose I right-clicked by mistake on that handle on the right of the lower node and made it the first node of the path – I might have. If so, it’s not OK for a BCP to be the first node, right?

This can only happen if you import the path from ufo.

No UFOs are involved here (ha ha) – it’s just my own stuff pasted from Ai, then modified quite a bit. I might have right-clicked by mistake on a handle instead of a node when zoomed out – although I don’t remember doing that. ◕ ¸ ◕

(But if it’s not OK for a handle to be the first “node”, maybe the program shouldn’t allow it from the outset).