@julian It's in a container created by the plugin which also is meant to tie it to the forum container. I think you are right that it can't interpret the address correctly as I just tried a clean install but this time with mongodb and that plugin and had the exact same issue.
You could make a custom icon just by making a new class in the css file something like
background-position: center center;
width: whatever maybe 16px or 32px
height: same as what you put above
Or you could make a custom font file