Music Editing - Balance not working

  • I have a rather strange phanomenon. I have been using Audacity for three months, mainly doing home recordings with guitar and voices. I do my recordings in Mono, however whenever recording several streams (like rhtyhm guitar, solo guitar, voice 1, voice 2 etc.) I use the so called PANORAMA (balance) to move one guitar more to the left and thee other more to the right. While doing so I use my headphones to actually hear "where"the sound is parked. Now this is not working anymore and I can find no reason. Whenever I use the balance now the sound is not moving from one sinde to the other but the volume is increasing or decreasing instead. Moreover, and this is very annoying, all my saved recordings which I saved as aup.files have been effected by this, i.e. I cannot hear them in the way I mixed them and all songs in aup. file format appear as one Mono sound in the middle of my headphones. They cannot be changed by using the balance. Who has an idea of what happened here?