When a grid is grouped by a field, and exported to pdf, then the column header titles are off by one. For example, if there are three fields A, B and C. And the grid is grouped by A, then when exporting to PDF, column B will have title C, and column C will have no title.
Reproduced here:
You'll see when clicking on "Export to PDF" below the grid that in the PDF export the true Name column title instead reads "Purchase", and the Purchase column has no title.