Futher to the problem, I wanted to eliminate the detail bands as a source of the problem. I created two reports bothe having identical layouts as far as groups and header fields and the same total band in the group footer (although in the second report it totals the class totals). Then I ran them twice - the first time I set it up like this:-

SELECT invoicehdr

SET RELATION TO invkey_pk INTO invoicelines, ;
                invkey_pk INTO invoiceclass ADDITIVE

SET SKIP TO invoicelines, invoiceclass

REPORT FORM linesreport PREVIEW

WAIT WINDOW "quick pause"

REPORT FORM classreport PREVIEW

This printed the extra lines on the second report the same as in the second detail band. I then made a quick change as follows:-

SET SKIP TO invoicelines

REPORT FORM linesreport PREVIEW

WAIT WINDOW "quick pause"

SET SKIP TO invoiceclass

REPORT FORM classreport PREVIEW

and this time the second report did NOT have any extra lines.

I still feel like I am missing something cause this couldn't be a bug in SKIP TO that has been hanging around all this time could it?