Installation works just fine for me, on 6.9.2
EDIT: @Squid when you uninstall the plugin and reinstall it it doesn't installs the package for the webgui.
Is this option wrong for installing the plugin: upgradepkg --install-new ?
EDIT2: @Squid Ah wait now I see it, I've forgot to implement the deinstallation from the package on deinstallation, added the webui on February and missed that probably.
Everything fixed.