ImgBurn and WinXP PRO x64

My Fujitsu/Siemens Amilo A 1667G laptop runs on WinXP x64 (fully updated with all the patches). The burner on the laptop is a Nec ND7551A and I also connected my older NEC ND6650A via a self-powered USB2 slimline enclosure. The problem is that the hardware buffer of the 7551 is always totally empty within ImgBurn, I don’t mean that it’s really empty as there are no slowdowns during the burn, but it is displayed as empty by ImgBurn, whereas the program properly displays the hardware buffer of the 6650. Both software buffers are displayed for both drives regardless of OS, this only happens on x64 Windows and only affects the 7551. Any ideas why is this happening?