I'm not sure, but I think perhaps the after insert my perhaps fire another before update by adding stuff to the existing record. I'd try the before update event of the form, which fires whenever a save operation is performed.
Easiest would be to add the extra fields to the form recordset, i e, have them bound, also add those as controls to the form, make them hidden (can be done from datasheet view through right clicking the column header, or with me!txtControl.columnhidden=true in for instance the on open/load event of the form) - or just bind the controls you have.
Then in the before update, assign appropriate values
[tt]me!txtControl.value = "some value..."[/tt]
- or execute some sql to update them.
Roy-Vidar