Follow up news.
I've installed drivers 16.12.2 and, so far, i haven't seen this sort of corruption, even though there's a mention of mouse corruption affecting RX480 users in the known issues, as pointed out by toxic80.
No replies in the
AMD's forum mouse corruption topic, after i posted my post there.
Dunno if it's related but something different is happening though, while playing grim dawn: when i alt-tab to the desktop to try and find the locations for the bounties, i type in the search engine (firefox, using duckduckgo) what i'm searching for but what i type appears VERY SLOWLY and while it hasn't caught up to what i've typed, i can't use the mouse to click on something else because it's locked in the writing cursor. The mouse moves but i can't select anything. After (what i typed) finishes appearing, the cursor becomes useable again. Don't have the camera handy to record this behaviour and won't be able to do so in the next few days, unfortunately.