This is with exactly the same test set-up, but with a KIA555P part in the socket (looking it up, it seems to be a Korea Electronics Corporation part). About 20ns of shoot-through for this part.
So, it looks like I was wrong and the sense resistor is doing fine.
This is with just the sense resistor and the other channel off, with its probe disconnected and the input set to the GND setting. It's more or less the same.
I'd doubt that the shoot-through current itself is actually bipolar. I suspect if the sense was better, with a much lower voltage drop, so that it was affecting the chip much less, and far less inductance hanging around, and the probing was better, it would disappear (but I can't really explain it, as it stands, other than that it feels to me like I'm looking at the lead inductances doing their thing).
Possibly, the breadboard may even help a little. With some impedance in the supply wires and a decoupling cap directly across the pins, it maybe helps isolate the supply system momentarily as the cap is doing the heavy work.
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