I can't explain so here's a screenshot

It does the same with longer pulses aswell but less often

Optifine is in aside some other fixing mods if that matters

happens only when doing ground => freestanding transitions and vise versa and its only visual

That's just render update lag between MCMultiPart wires and non-MCMultiPart wires, I think. Not sure if I can do anything about it.

Indeed it only happens between charset and Multipart, its only visual so i don't think its fatal