SMS to multiple recipients sent as MMS - costs incurred

/e/ version: 0.9-202051554230
Device model: Oneplus 3t
When it started to occur: since install?
Reproducible with the last /e/ version:
Reproducible with LineageOS:

Summary

Plain, basic text SMS written and sent from default app to multiple recipients (but not as 'Group message' are charged by telco as multiple MMS (which in my case are not included in contract so cost me money)

The device is unusable
The bug is the source of a data loss or a big waste of time (if time is money)
The bug concerns a third-party application
The bug concerns security
The bug concerns privacy

The problem

Steps to reproduce Send plain text (no special characters etc) to multiple recipients

What is the current behavior? Get charged 0.3GBP per recipient, but only realise at the end of the month after it has all mounted up... Say some very rude words out of frustration. Looking at message details confirms that they are in fact MMS.

What is the expected correct behavior? SMSes are sent and received as SMS...

Technical informations

Relevant logs (adb logcat) No need...

Relevant screenshots

Solutions

Workaround

Possible fixes