Preventing automatic behavior in PulseAudio

[Aleks]

I have this problem from quite long ago with various OS installations. Sometimes it goes away for a while and then it comes back, a weird thing. Namely, if the output volume is high, the input jumps from line in to rear or front mic, or from rear mic to front mic etc. This is especially a problem when using Skype, but also when I plug a guitar in line in. Is there a way to prevent this behavior?