Here's some test code:
New Window("Test",
Border Box(Top(20),Bottom(20),Left(20),Right(20),
LineupBox(NCol(2),
Text Box("First Name", <<Vertical Alignment("Center")),
Text Edit Box("",<<Set Font Size(12), <<Set Width(300)),
Text Box("Surname", <<Vertical Alignment("Center")),
Text Edit Box("",<<Set Font Size(12), <<Set Width(300)),
)
)
)
Depending on how you enter a text field (mouse-click or tab) and based on time of day or some other random event I get either the font size I requested, or not ...

The small font size only occurs at the time when input is typed, but its still inconsistent and ugly.
I initially assumed it was a JMP 13 issue because there is a lot of inconsistent font behaviour for display boxes in this release but that's not the case - it also occurs with version 12.
Any ideas as to what is going on?