This change was introduced within new general ledger engine.
General ledger was completely rewritten to address performance issues, all known inventory / forex bugs, expanded custom reports and many other subtle improvements (e.g. when drilling-down into transactions, you will see more relevant columns based on the context).
This was a case when a bug has became a feature for some users. When you rely on broken behaviour and it gets fixed, it will cause some grief.
In your referenced topic, the user was using GST 10% on accounts receivable as a way to multiply tax-exclusive amount.
If you need to multiply tax-exclusive amount, just use formula within the field as per:
https://www.manager.io/guides/18222
For example, instead of entering 100 and selecting tax code to get 110. You could have just typed 100*1.1