Default distribution account is grayed out and skipped (tabbed over) on certain suppliers, what cont

Oracle Payables R12.2.5

When entering invoices on most of our vendors, we can tab directly from the Amount field to the Default Distribution Account as demonstrated below.

However on certain vendors, the Default Distribution Account is grayed out.  Tabbing results in this field being skipped.  However, if we use the mouse and place the cursor in that field, it turns white and allows entry.

My question is, what controls this behavior?  I'd assume it is something with the supplier setup but I can't see anything obvious.

We are using a custom folder/view, but we are not using any form personalizations.