Should be simple but I'm rusty..

In a Form.Init() I create a cursor:

CREATE CURSOR xxx (
    MyField N(6,1)
)
APPE BLANK

If I open this in a browse window I can enter data as expected (e.g. typing '12345' gives '1234.5').
In the form I have a textbox with DataSource = xxx.MyField.
If I enter the same keystrokes here I get '1.24' and it tabs to the next item.

What am I missing?