I thought you were referring to the VCTL input only, but it seems to apply to the ANT port as well assuming there is an ESD protection diode on that input. Again, I am way out of my league, but would that make sense?
I made a hypothesis based on the ADRF5022 interface. I don’t think the RF port has a diode in it because of the higher losses.
My conclusion from the experiments with BLE is that on-board antenna work well enough if used with proper power supply to RF switch.
Your experimental results also show that on-board antennas can be used without problems if the RF switch is properly powered and the antenna is correctly selected.