I have fixed the issue. Turns out this is a "feature" in KDE now.
One other small thing we did in 4.7 on the panel is make the default launchers in the taskbar for file manager and web browser follow your prefered applications as set in the system settings. Which means we have one configuration that we ship, but it matches what you want. Including if you change your mind later. Since they share space intelligently with the tasks, it means less space used: when the app is running, the launcher goes away. (Btw, a bug in 4.7.0 around that feature has been fixed for 4.7.1, so if that isn't working for you properly, the fix is just a patch level update away.) So you can either change your browser and file manager to whatever you prefer and keep it on the panel or you can edit ~.kde/share/config/plasma-desktop-appletsrc and delete the 2 lines that mention " preferred browser" and "preferred file manager". After this you can relog and it will be fixed. I guess this can be closed since it's not really a "bug" according to KDE upstream. I found all this info at https://bbs.archlinux.org/viewtopic.php?id=123833
