Thank you for your feedback Maestro and Conductor...

I've tried to right-click on the cell in F/R and do a format|borders to see what borders are selected but the only indented button is always the left! If I change all the borders to something obvious (thick line) and go back to edit, only the left button is selected and with a thin line. This seems to be the default on every cell in the sheet...

Either way, this will probably not solve the problem of rendering when converting to PDF. You're right, this seems to also happen in Excel and other software and PDFs do not seem able to exactly duplicate the print version.