Game log scrolling backwards on hover

[MrSwede]

I'm not even sure if this is a bug or some option I've just accidentally toggled without noticing, but either way I need some help.

So, I was clearing the sand worm lair with my latest character when the message log started weirding out on me.

Essentially, it doesn't update properly in normal use (the UI element doesn't always show whatever's actually happening in-game, sometimes just staying blank while the game progresses), but when I hover the cursor over that part of the screen, it starts automatically scrolling the entire game log backwards, from newest to earliest.
Then, once it stops at the game start message (sometimes I don't even get one, in which case it's just the first thing that happened. A rest or something), any further updates cause it to scroll down "normally", except from the top, scrolling down the earliest messages in the log at the same pace as the new entries that should be appearing at the bottom (opening the separate log window shows everything normally).
This continues until I hover the cursor over the element again, whereupon it starts scrolling back up, then repeats.

I've never seen this before, and going through the menus, I haven't found any options that might explain this.
Have I just screwed something up, or is this a genuine bug?