>When fields are filled in on the parent table record, and the cursor is moved to the child table grid, does a TABLEUPDATE() occur on the parent table record? (Because of the change in SELECTed table.)
>

In my experience, yes. There are a few controls that cause the current record in a Row buffered cursor to be written. This is one of the many reasons to NEVER use row buffering. It's just too unpredictable.