Odd - I just tested on one icon on mine (3.9.1987~gc053acd) and it seemed to work fine. And your installation must be getting the picons fromsomewhere - tvh has no knowledge (as far as I know!) of some universal website full of icons.
More testing... yes, I see what you mean. I can remove a user (file://) icon, and I immediately get the picon. If I disable picons, this makes now difference and the picon:// path still appears. I switched off image caching, but that made no difference: I didn't clean my image cache, though, which may be relevant.
It could be a bug, or it could be something getting cached so it survives to be used again. Thoughts include removing the picon path, disabling and clearing the cache and restarting tvh before resetting the icons - or simply deleting the picons you have downloaded, as they're clearly stored somewhere where your tvh instance can find them.
