Line-in of CM106 like sound device does not work

[Sietse Achterop <s.achterop@rug.nl>]

  Dear List,

Using Wheezy, version 7.3, with the 3.11 kernel from wheezy-backports,
I have an exteral USB sound device from Sweex, see
   http://www.sweex.com/nl/assortiment/sound-vision/sound-cards/sc016/

lsusb says:
   Bus 003 Device 004: ID 0d8c:0102 C-Media Electronics, Inc. CM106 Like Sound Device
This hardware seems OK, because under Windows it is working properly.

The problem is that no signal is seen from the line-in input.
The microphone input (and output) work ok.
I can set the settings from System Settings->Sound.
The microphone-led on the device shows that the setting is changed on the device.
  (I am using pulseaudio, so it can also use pavucontrol)

The question of course is, why are signals on line-in not seen?
What could wrong?

  Thanks in advance,
      Sietse