Bridge chooses IPv6 instead of IPv4 (as configured) for server transport 'obfs4'

Running a bridge at a Debian (buster stable) with 0.4.3.6-1~d10.buster+1 and 0.0.7-4+b12 brought the issue that configuring the server transport 'obfs4' according to the official Tor documentation to listen at IPv4 as

ServerTransportListenAddr obfs4 0.0.0.0:443

let the bridge choose IPv6:

Aug 16 09:44:57.000 [notice] Registered server transport 'obfs4' at '[::]:443'

I set ServerTransportListenAddr to the real IP address which helped:

# we have to explicitly set this (and NOT to "0.0.0.0:443" and "[..]:443" respectively)
ServerTransportListenAddr obfs4 <ip addr>:<obfs4 port>

This bridge behaviour effectively turnes the bridge in being unusable for obfs4 connections for me. I tested the above with a connection from a local Tor client and from within Tails from a client location where only IPv4 was working.