This feature worked once in the mists of time when I was testing OMV and long before I started using it live (I think it was early 0.5 Sardaukar) but after a reinstall on different hardware it never worked again. Here we are on OMV 1.0 and I've got a little bit of time to try and track the issue down.
Pretty much any plugin, Couchpotato, SABnzbd, Sonarr, Sickbeard, Subsonic, you name it, if it's got a "Show tab containing XXXXXXX web interface frame." checkbox, then when you check it and go to the tab, there's absolutely nothing, just a white empty box. All of these plugins are fully functional (excepting Sickbeard as I'm using Sonaar at the moment) and can be reached by the "Show Web Interface" button or by directly going to the URL (works both ways). Settings are saved persistently through reboots - the tab's still there afterwards, but nothing shows up.
Does anyone have any ideas what might cause this? Perhaps more importantly, is it worth the aggravation to bother? I have to access my OMV from the outside on port 443 ONLY, as every other high outbound port is blocked by MIS. So if I wanted to, for example, hit Couchpotato from the outside world, but sending to port 5050 is blocked on my work network, will the interface frame send it out via 443 along with the rest of the HTTPS session? If it doesn't, there's very little reason for me to bother, except to solve the issue due to curiosity.