This is the default behavior.
If you do not set the id send from the server the jqGrid add row with a number of records + 1. So it is possible in this case to have duplicate id’s.
You can use the third parameter in afterSubmit row event to set the correct id (i.e. the id from the server)

For more info see docs

Regards
Tony

Mike,
afterSubmit accept two parameter (as of the docs)
the first one is the data returned from the server.
This data can be in in what you want format. You should get this data – transform it to array and send it back to jqGrid.

Here is a brief example.
Lets suppose that you return from server the flowing data
success;the_newid (I suppose all is ok – succes)
then

afterSubmit: function(server_data, posted_data) {
result = server_data.responseText.split(“;”)
if (result[0] == “success”)
return [true,””,result[1]];
else return [false,”Error inserting row”];
}

Enjoy
Tony