MQTT bug "forced conversion to string?"

[Surfer2010]

Systemdata	Bitte Ausfüllen
Hardwaresystem:	NUC
Arbeitsspeicher:	4GB
Festplattenart:	SSD
Betriebssystem:	Debian
Image genutzt:	Ja DockerContainer
Ort/Name der Imagedatei:	https://github.com/buanet/ioBroker.docker

The Problem is, i want to get a MAP sent as a base64 decoded png.

Valetudo Robot

Decode by "I can't believe it's not valetudo" (https://github.com/Hypfer/ICantBelieveItsNotValetudo/blob/54cc0d96a6c03ee4dc92b86e533c0cd3999a7068/lib/MqttClient.js#L133)

ErrorMessage:
https://pastebin.com/bUPTaiPc

The Programmer of Valetudo & ICANTBELIEVEITSNOTVALETUDO says:

then I'd assume that their mqtt broker implementation is broken
yeah pretty sure that it's a bug in that
https://github.com/ioBroker/ioBroker.mqtt/blob/master/lib/server.js

somewhere something is forcefully transforming the topics payload to a string
which is not according to MQTT spec

yep
https://github.com/ioBroker/ioBroker.mqtt/blob/556e60f30cbe5ae3571a8738eb6e927ee9c0ad98/lib/server.js#L481-L502

I'd guess that it's this code
although I haven't thoroughly understood the whole module yet
it just looks like it would cause this

Is this a bug/intentional? Can this be fixed?
Thanks for your help