Audio delay meter keeps decreasing

I’m not sure if this is a bug or normal behaviour

Since the latest update I’ve noticed that if I press the info button during playback the audio delay indicator (I’m assuming that’s what it is) keeps decreasing. It’s the first parameter next to the C labelled ad:-

It does not affect audio/video sync so I’m not sure what it’s measuring.

This happens when playing back video with audio out set to hdmi, it does not happen if I’m using the HifiBerry DAC+ I always have the audio delay preference set to -100ms when I’m using the DAC this setting is reflected in the ad:- parameter, this is why why I’m assuming it’s an audio delay indicator.

Just to be clear, the audio delay preference is set to 0 when audio out is set to hdmi

Also the aq:- parameter seems to constantly decrease as well, don’t know if that’s related?