AC3 sounds softer and muddier than FLAC (otherwise same content!)

[The Bright Side]

I noticed on Linux Mint 19.3 that some Dolby Digital (AC3 aka A/52) 5.1 tracks play much softer and muddier than the exact same content decoded to FLAC. The same is not true for other media players, like Parole. Happens using PulseAudio. Here's a video where you can clearly hear the difference:

https://youtu.be/zMZ5jYrm3ec

This example shows a track from the Billy Joel DVD, "The Essential Video Collection". Other titles, like Whitesnake's "Live at Donington" in Dolby Digital 5.1, don't exhibit the same behaviour. I'm wondering if some AC3 soundtracks have certain normalization flags in them that cause this?

Things I tried to no avail:
- Disabling A/52 dynamic range compression in VLC's audio codecs settings
- Removing the audio normalization flag from the AC3 using MKVtoolnix

Is this a bug or a feature? If the latter, how do I disable it?