Got a surprise today when I ran ERC on a schematic after upgrading to KiCad 9. My “unconnected” wires with net labels were getting flagged as actually unconnected wires. I checked using Highlight Nets to make sure the nets I thought were electrically connected via labeling were actually connected, and they were.

So KiCad knew the label referred to the wire, but it was also claiming it wasn’t.

Huh?

This same schematic had passed ERC before (in KiCad 8). So I knew it should be a change introduced in 9. I hunted this strangeness down on the web and sure enough, KiCad 9 now flags “unconnected” wires with net labels that (as evidenced by Highlight Nets) it kinda knows they’re associated with, unless the label is associated with the wire in a specific way.

KiCad is now demanding that the little square handle (on the bottom left or right of a selected net label connect to the endpoint of the wire for it to not throw an error on ERC. For example, I clicked on the R_RST net label and you can see the little ‘+’ at its bottom right. that needs to be aligned to coincide with the end of the wire it’s labeling.

Of course, since the + is on the bottom left, dragging it to coincide with the end of the wire would result in a funny-looking labeling scheme. But if we hit the ‘x’ key while the label is selected, the ‘+’ moves to the side of the label that’s appropriate for the wire that it’s associated with (but not associated with).

So click ‘x’:

And now we can drag the label to make the ‘+’ and wire end coincident and it looks normal.

And if we re-run ERC… voila! The net label is now both associated with the wire and associated with the wire.

Now my first thought when I figured this out was “Why are they fixing something that was working fine?“

Then my medical device everything-should-be-deterministic-brain kicked in and thought “Oh yeah, you’ve wondered in the past how it knows which label goes with which wire – what’s the algorithm it used to infer it?” Well now we know for sure as the connection needs to be made explicitly. A bit more work, but less room for oopsies.
I mentioned this to an EE I know, one who does a lot more EE than I do these days, and she confirmed that sometimes people have gotten burned by net labels associating themselves to the wrong pin.

So, a good change but a little surprise to work out.