On one band only? It only does this on 40m.
Depends on the design of the particular rig. Those that have different power switching schemes for various functions, often via the bandswitching, may indeed exhibit the problem on only one band or more.
Studying the schematic and tracing the thing down can find that possibility or rule it out.
Keyword is "possibility" - troubleshooting is detective work, to my way of thinking, each possibility must be investigated but it has also been my experience that I get into trouble when blanket ruling something out altogether before investigating. Then there's old man Occam to consider as well.
Tracing backwards with the 'scope may pinpoint the problem a lot quicker.