Base report--mystery gap at top of page

I’m using LO 3.5.7.2 base. I created a report with the Report Wizard, then opened it in the report designer to make modifications–namely, removing the author/date information and making the report two columns.

When I go to print preview, the first column of the report starts about 1/2" down from my specified page margin, but the second column starts in the right location. If I go down to one column, it still exhibits this behavior. It appears that the report insists on leaving 1/2" of whitespace before the start of the actual chart. What’s wrong?