>i think the bottomline of my question is: Is grid style data entry not advisable especially if the record buildup becomes large because it triggers unpredictable behaviours in the grid cell?

Why not have an "invoice" type entry on the form as well as a grid (maybe ReadOnly). As you write (or add) invoices, refresh the the grid. The user gets the best of both: A controlled invoice entry form, and a 'list' of whats been entered to point (for reconciliation)!