In case anyone was wondering, the input-pin-to-GND diode has excellent hFE:
So, if you use the input ESD diodes to clamp a negative-going signal, the clamp current is essentially cascoded into VDD. Expect a proportional increase in supply current!
This BJT in turn forms an SCR with nearby P wells. hFE depends on Vce, so it doesn't latch up when fully saturating into a 60 ohm load resistor, but latches above about 80mA with Vce = 10V. Latchup current is around 280mA for this part.
Analogously, the input-VDD diodes also have hFE (PNP from input (emitter) to VDD (base) to VSS (collector)), but it's small, about 0.5.
HEF4011BP shows a little crosstalk between input pins within a gate: hFE ~0.035 (for the Vdd diodes; none for the Vss diodes). 74HC shows a similar effect. No crosstalk between gates.