On my QMX, I observed that the "garbage graphs" happened if I tried to step through the bands too rapidly, i.e., if I was on 20m and stepped up to 10m slowly, one graph at a time, all was well, but if I tried to go straight to 10m by stepping rapidly, interrupting a graph before it was done, I'd get junk.? As I recall, the solution was to power cycle the QMX and be more patient :-).
