The explanation is described here:
Instead, the Windows GDI display information is passed to your Windows print driver--which in this case is actually the RIP, the raster image processor itself for this marking engine. Once the RIP is finished (it uses your host computer's power to do all the work in turning your document into a laser bitmap), it sends the bitmap to the marking engine over the USB cable.
The workaround is to use a WinXP machine as the print server, and install the PagePro 1400W on your Windows 7 machine (http://printer.konicaminolta.com/support/current_printers/PP1400W_sup.htm#Drivers) You must also disable Bidirectional Printing since the printer driver tries to get an acknowledgment back from the printer before printing the full document. The steps to setup the print server is described below: