I attached the UD-3900 to my surface and the two external displays are sharing the extended desktop. The surface has the main screen and the two externals both show the same duplicated extended desktop.
Thanks for the post! I’m sorry your docking station isn’t working as expected, but I’m happy to help. Based on the information you’ve provided I’d like to start by making sure that your display settings are set correctly. To do this lets start by right clicking the desktop, selecting “Display Settings” and if I’m correct you should only see 2 boxes to represent the monitors. One will have a number 1 on it and the other should look like 2|3. Click on the one with two numbers and scroll down to where it says “Multiple displays”. From there click on the drop down box and select “Extend desktop on 2 and 3”. From there, click “apply” and that should allow you to have extended monitors.
If that does not work, please let me know, and we’ll take it from there.