I changed the patch cable ( which I bought new) with my another old one and as yet, I hear no problem.....
I did that too, but it only worked temporarily. I cleaned the jacks with de-oxit (then inserting/pulling out a cord 1,000 times)
My #1 MP-2 started doing this about 2 months ago, seemingly at random. I cleaned the jacks and switches as best I could and hoped for the best. However, it still happened randomly so I bought another MP-2 for backup. Wouldn't you know, the #2 unit
did the same thing. Now, I'm experimenting by actually using BOTH MP-2s in my Live Rig. #1 is used as a preamp/compressor for the EHX "9" pedal section of my rig, and #2 is my guitar preamp. #1 has nothing in its Loops, and is currently working flawlessly there. #2 continued to do the Volume Increase at random, and it is using the Loops. The last time it happened, I reached back there and wiggled stuff around while it was acting up and appeared that one of the patch cables was causing it. I pulled that particular pair of cables (shit Radio Shack ones) out and replaced them with new cables of a better quality. Since then, it has only happened once so far and just a little wiggle of the cable inside the jack fixed it.
I have concluded that the problem must be within the jack itself, and not the cables or switch.