sms messages deleted from dlr table

Dear Kannel Devel,

I've been using mysql with the dlr table using group = mysql-connection, and
set a primary key to autoincrement. I've found that the primary key seems to
to skip an increment for example at 10 the next entry will 12. Could this be
because when SMSs are delivered the SMSs are deleted from the DLR table.
1)Is this the probable cause of this as mysql should never skip an increment
unless it was placed in the table and deleted?
2)Is there any way to configure the group = mysql-connection to stop SMSs
from being deleted, or is there any other way to stop SMSs being
automatically deleted?

Thanks