Equations in text cell in wrong format

In order to type an equation in a text cell one presses Ctrl+9 and then you get a highlighted region into which you type an equation. Here is an example

The problem here is that the equation is in an Arial font. Equations should appear in TraditionalForm. If I go to a new cell make it TranditionalForm and type I get this:

This is what I want (except that it is annoyingly in bold which I have removed).

The real mystery is if I do ShowExpression on the text cell I get

Note that the Cell within the Cell containing the equation has "FormatType" "TraditionalForm". So the question: why is the equation in the text cell not in TraditioalForm?

If I do ShowExpression on the equation in the TraditionalForm cell I get this

This is almost the same except it has an extra StyleBox. Has this been missed out? This is version 12.2 but this problem has been around for several versions.

How do I fix this?

Some similar question asked before are here and here but are not quite the same.