I cannot print duplex on B4-sized paper on MFC J6510DW

I cannot print duplex on B4-sized paper on MFC J6510DW

I have a print job on B4-sized paper (250x350mm) that I would like to print duplex from Microsoft Publisher or Adobe .pdf. When I try to print duplex, while the programs happily accept the instruction to print duplex, the printer will not print duplex on B4 paper. I can print duplex on A4 and A3, however.