Hi Bill
I'm not sure what you mean by "other table operations which use max/min, etc are executing without being explicitly called in the rule". If you embed a min/max table operation inside another expression then you are explicitly executing that table operation.
Just taking another look at your screenshots, it seems you were using the ruleset variable in your db lookup, rather than embedding an expression. Unfortunately, you can't directly embed the GET_IP_DOC_NUMBER table operation into your db lookup as the table operation returns a structure not an element. Off the top of my head, I don't know of a way to use a table operation expression (that returns a structure) inside your db lookup but I suspect it can't be done and that the way you have built it now might be the only way. If I find some time, I'll have a play and see if I can prove it. Otherwise, good luck with it all.
Kind Regards
Glen