Why does this idiot machine do things you don't tell it to?

I go into midi files on my hard drive to adjust them while it's playing, therefore using the master track, and the damn thing indiscrimnately changes volumes on me. Why?

One example. I go into track 1 to change a Fingered bass to a deep bass. NOTHING ELSE. The volume is at 45. I start the song to listen after it finshes saving and guess what? The volume is now 63. Too damn loud. So I try to drop the volume on the master track and save again. What does it do? Puts it right back up to 63 again. Completely ignoring me.

On another song, I wasn't even touching volumes, but changing instruments again. About 7 instruments dropped in volume. Some went down as far as about 16 when it was originally 55. What in God's name could be the reason for this? I would be about 5 times more ahead by now on my midi files being converted if thus stupid machine didn't do things like this.

does anyone have any idea why? It doesn't seem to do it to every sequence, just some.

I'd appreciate some help before I chuck this thing out the window. I don't need this aggravation.