The DisplayLink GUI can display resolutions that the Windows Display Properties dialogue box will not display. This happens with resolutions below 640 pixels wide and 480 pixels high.

Windows Display Properties (WDP) does not like modes smaller than 800x600, but can show them (especially if the current mode is between 640 and 800 pixels wide, and 480 and 600 pixels tall).

Modes smaller than 640x480 are never shown, and WDP will try to change it to a higher mode. If the currently selected mode is smaller than the (eg 720x400), the mode will be shown as 640x480 in Windows Display Properties. The display position will also be show incorrectly at the top left of the display layout.

To resolve:

This is a limitation of Windows Display Properties. Smaller displays should be managed through the DisplayLink GUI to set the mode and position. Alternativly, 3rd party software will support displays with small resolutions, for example Ultramon.