Hi,
the better idea would be to use an unbound form in this case and create the record in table 1 like you already do in button 2 for table 2. In this case you should not get in trouble.
But if you have a record structure which can be used in table 1 and table 2 I guess there is a problem in your data structure as in this case you normally only need to have one table with maybe an additional field to separate table1-data from table2-data.
In this case you can simply use a bound form and create this id in dependence of which button was clicked.
Cheers,
Christian