I don't know about any magic, but whenever I test some icons or rules, I just restart fm with
killall fm; (fm -b &)
Thanks, that may solve a different problem I occasionally have ... would probably solve this one too but
My own bad description. Occasionally when I have several file windows open, for no apparent reason one of them will suddenly decide to display as a text list of files. Hmm. Force it to display as icons and nothing shows. Back to 'display as a list' and everything shows up fine. Display as icons, nothing there. I figured out some little gimmick to make the window display as icons again without a logout - login sequence or restarting fm.
Just can't remember what it was