No, it is not a problem with your soundcard. What happened was that for Vista, Microsoft completely re-architectured the sound system and volume control. Now, instead of having separate mixers for different devices (wave, midi, cd, etc.) there is only a single mixer for each application.
Obviously this is quite inconvenient for some people and not even noticed by others. For those of use for whom it is a problem, unfortunately there are no practical solutions and instead, it has to be somehow worked-around by rearranging things to work with applications instead of devices.
(I looked high and low for a solution because in XP, I had assigned a hotkey to the line-in device so that I could use easily adjust the volume of my TV tuner, but in 7, there was no way around it. I ended up having to settle for assigning the hotkey to adjust the volume of the TV application itself which in this case wasn’t too bad since I mainly used just one program, but it meant that I was grossly inconvenienced if I wanted to use another program like VirtualDub, etc.)
Interestingly enough, there are more people trying to do the opposite (get Vista’s application-specific volume in XP) with hardly any more success—there are one or two program that let you do it, but not very well.