A printable form was set as non-default and then deleted. Nevertheless, it reappeared as default.
There are a number of printable forms which are created in OBAS by default and cannot be removed.
If, say Credit invoice details printable form was set as non-default and later removed it will be recreated automatically as default. That behaviour is by design.
If a printable form was created manually as non-default ("Is default printable form" checkbox was left unchecked during the form creation), the form will not be recreated upon removal.