Proposal patch here
Different window iconized with multihead + current monitor only
I can confirm this with lxpanel GIT head. The attached patch should fix this issue.
Looks like this is fixed in lxpanel 0.9.0 (ref: https://sourceforge.net/p/lxde/bugs/798/ ), while you are using lxpanel 0.8.1. It would be better that you ask the vendor side maintainer to upgrade lxpanel.
Okay, thank you for review. I think your idea is much better, and I think the (newly) attached patch should follow your idea. Note that currently with this patch, I left APIs (of symbols) which are already visible outside unchanged, so I added some "wrapper" functions. And this is "thermal" plugin, not "cpu"... sorry.
lxpanel/cpu: panel font size configuration not honored
lxpanel/weather: does not honor panel font config immediately