Edit Masks & Cursor positions in PhAB

I’m not sure if this is the right group to ask, but here goes…

I’m working on a UI in PhAB, with user-editable text boxes. I want to
restrict the text to numbers via an edit mask, which works fine. But
when I run the program and click on the text box, the cursor
automatically goes to the end and won’t let me input anything until I
arrow back to the beginning. I’ve tried playing with
Pt_ARG_CURSOR_POSITION, but that doesn’t seem to make a difference. It
also doesn’t care whether I initially have a text string or not.

thanks,
Meredith Dill