Editor buttons plugin - buttons not shown

I just installed the editor buttons plugin, but the buttons don't show. I have the most recent admin plugin installed. The editor buttons settings claim are all set so they should be shown. IWhat's a good starting point for debugging this?

fyi, I tried rm -rf cache/*, but that didn't help.

I just tested, installed on a clean skeleton, it works just right after installing:

Screen Shot 2015-11-02 at 14

Ok, found the problem now. The button js code was constructing URLs using $this->grav['base_url_absolute'], which returns a string without the port number. I was running the webserver on port 9980, and nothing was listening on port 80. I guess most of grav uses relative paths, and that's why I didn't notice this before.

Ah, and now I realised that the problem lies in my using vagrant to forward port 80 on the virtual machine to 9980 on my actual machine. So my own fault entirely...