On descent, the autothrottle disconnect switch on the thrust lever does not seem to operate while in VNAV.

The FMA displays SPD autothrottle mode and briefly flashes but remains on when the disconnect is pressed.

Also, if the A/T ARM switch on the MCP is OFF, with the autopilot in V/S mode, pressing VNAV still arms the A/T and the FMA SPD mode.
VNAV can't be used independently from autothrottle.

Video: https://www.youtube.com/watch?v=JMS3mM1_DXo (Timestamps of inputs in the description)

Can anyone reproduce this?