Walking inside of scaffolding that has air below it doesn't produce any footstep sounds or subtitles

The Bug:

Walking inside of scaffolding that has air below it doesn't produce any footstep sounds or subtitles.

Steps to Reproduce:

1. Build the setup as shown in the attachment below. setup.png
2. Enable subtitles in your accessibility settings if not already done.
3. Walk inside of the scaffolding that has the magenta concrete one block below it and listen closely as you move around.
4. Take note as to whether or not walking inside of scaffolding that has air below it produces any footstep sounds or subtitles.

Observed Behavior:

Footstep sounds and subtitles aren't produced.

Expected Behavior:

Footstep sounds and subtitles would be produced.