It could be the case that your Windows Audio Pan settings are not set correctly and only either the Left channel is recording, the Right channel or an un-balanced signal of both.
To correct this go to your Windows Audio Preferences either via the Control Panel Window or by right clicking the Speaker icon in the bottom right hand side of the task bar (as seen in the image below), then select 'Recording devices'.
From the 'Sound' window that pops up select the Behringer WDM driver and click the 'Properties' button. A window named 'Line In Properties' will show, click the 'Balance' button. A 'Balance' box pops up where you can then change the settings for Line Inputs 1 and 2 (i.e 'Left' side and 'Right' side respectively). If you want both the Left and Right channels to come through the Line Input simply push the faders to full at 100. If you want only the left channel to record simply lower the Right side (2) to 0 (and vice versa if you want only the Right channel to record). See the image below for an illustration: