I hadnt realized that! I just looked at game i'm playing, and that is the way it's shown. If I want to see trace to different hex I have to turn off supply trace mode, select the desired supply source, then turn supply source trace back on. It is also reflected in the action point cost.
This could be important to know for large maps with potentially complex supply situation.
I started to suggest changing this, but the more I thought about the alternatives, the less attractive any of the alternatives appeared, and the more it looks like the way it's implemented is probably fine with me.
One feature enhancement might be that when you dont have supply trace turned on, if you select a unit, and then right click (right now right-clicking unit on map display doesnt do anything different thatn left clicking as far as I can tell), you see the actual supply trace for that unit. I haven't really examined this idea, so it might have some pitfalls as well, but it's athough. But for now, I'm fine with what it shows. Perhaps I'll add this paragraph to the "wish list thread".
Thanks for highlighting this. Ive about decided, that now that I've played the game some more, I need to re-read the manual.