Which one of the tables is a parent table?

>Let's say we have 2 tables, TRANS and MAST.
>Add the tables to a DE in a form, and drag/drop the key field to create a relation.
>Do not set the OneToMany prop of the relation to .T.
>
>First scenario:
>Add a grid for the TRANS table to the form.
>Add a text box bound to any field in the MAST to the form.
>Run the form.
>What I consider odd is that as you arrow up and down through the grid, the textbox will not show the correct value in the Master. The record pointer in the master does not move according to the relation.
>
>Second scenario:
>Now, add a grid of the MAST to the form - do not change anything.
>Run the form, and move trough the TRANS grid.
>The text box will show the right value, and the MAST grid will refresh, the record pointer is now moving.
>
>Epilogue:
>Setting the OneToMany prop of the relation to .T., will fix the problem in the first scenario too.
>All this makes some sense, but not quite... Can anybody explain what prevents the record pointer to move in the first scenario?
>
>TIA