Thank you Bob, we are a bunch of passionate people in this company and a few positive feedback from time to time makes it worthy!
Before 1.7b4 the Mac driver was incorrectly limiting the resolution on a particular chip variant. The maximum resolution still depends on the chip used in the device.
Googling around the advertised max resolution for the BVUMD3 is 1920x1080 so it should be a DL-165 chip that on both Mac and Windows should not be able to show 1920x1200.
For a 1920x1200 resolution you need a device that actually supports it.
The easiest way to find one is going to the DL shop and look for devices that advertise a maximum resolution of 2048x1152 or 1920x1200, these have a DL-195. The link is
http://www.displaylink.com/shop/index.php