More than likely, if it isn't a bug, its your lack of understanding. FreeBSD seems to have a pretty steep learning curve if you've never used it before. I hate telling people to RTFM, but in this case you may have to. I praise the manual regularly as I think it is very well written, it also leaves alot of stuff up to the admin to have knowledge in. This is partially by design, as well as how FreeBSD is built. FreeBSD will let you do things that are completely idiotic if you don't know what you are doing. The expectation is that you really do know what stuff does before you tinker.
Lots of people have been in this forum with lost data because they made a zpool with drives in a RAIDZ2, then added 1 more disk thinking they could expand the VDev. VDevs don't expand, and when that 1 disk fails they lose the whole pool and have a dumbfounded look on their face. That's partly why I created the guide for noobies. My heart sinks a little when I see someone start a thread with "So did I just lose 10TB of data?"
Anyway, back to your issue. Can you post a screenshot of what you see when you expand the plugins?