This happens to me all the time. If you roll over something that comes up with a description box it has a chance of not going away. I used to get this all the time from the sound *on which seems to be your issue too, so I just muted the entire miniclient instead so I never had to roll over it. It does come up really often in mines though, the boxes for ores will be in the center of my screen for a while.

If you refresh the page it goes away.

If you hover back over the thing that causes the dialogue box it'll go away.