Flashed with all released 1640 (.cvt) firmwares to no avail, uninstalled QSuite2, cleaned the registry, but still nogo...
W*f. I had nothing to lose, so I decided to flash back with latest Philips 1648 (.cvt) firmware and WinDWFlash.
And you know what? The drivename changed..., to Philips 1648 ofcourse, but that's not a big deal because I knew the flash back to BenQ 1640 from Philips was working... heh he.
Finally managed to flash 1640 firmware and now the ID string shows DW1640 again.
Sorry for interrupting your reading.