Text box font size not working correctly on bindings

Designer on win 10.

The text font size in a text box seems to have no effect in designer if it is bound to a variable. If fixed text it works as expected. The text is fixed at around 14pt - always.

There’s more !!!
The font size change DOES show up on Android phone but NOT on the Designer Simulator. This is a workaround but does necessitate a few test runs on Android to get it right.

Is this a bug or just something the simulator does not faithfully reproduce?