avr64ea28: analogReadDiff() throws badArg("Invalid negative pin - valid options are ... PORTA."); for Port A pins

[wke67]

here is the example sketch:

void setup() {
  long w;
  w=analogReadDiff(PIN_PA4, PIN_PA5);
  Serial.printf("%ld \n", w);
}
void loop() {
}

Compiler throws:

In function 'check_valid_negative_pin',
inlined from 'analogReadDiff.constprop' at ~/.arduino15/packages/DxCore/hardware/megaavr/1.6.2/cores/dxcore/wiring_analog.c:630:5,
inlined from 'setup' at ~/Arduino/sketchbook/sketch_apr25b/sketch_apr25b.ino:4:4,
inlined from 'main' at ~/.arduino15/packages/DxCore/hardware/megaavr/1.6.2/cores/dxcore/main.cpp:95:8:
~/.arduino15/packages/DxCore/hardware/megaavr/1.6.2/cores/dxcore/wiring_analog.c:452:9: error: call to 'badArg' declared with attribute error:
badArg("Invalid negative pin - valid options are ADC_GROUND, ADC_VDDDIV10, ADC_DACREF0, or any pin on PORTA.");

I believe in line 630 in wiring_analog.c the call to check_valid_negative_pin(neg) should be check_valid_analog_pin(neg) since there is no difference between muxneg and muxpos in Ex types. I also don't understand the logic in check_valid_negative_pin(neg), is it looking at pins or channels?