Originally posted in the forum with way more detail there:
http://forum.terasology.org/threads/strange-constant-diagonal-artifacting.1565/
Youtube video showing the issue:
https://www.youtube.com/watch?v=W9qMbXBdS0s
Some interesting details:
At this point it might also be an hardware/drivers specific problem as only one person reported the issue.
@Cervator: can you assign me and @tdgunes on it?
Thank you @SkySom!
Another case. I am not able to open my inventory either, might be connected. I was trying to place water down to replace this issue.
EDIT: as pointed out by Cervator, there's no water if you run no modules, so it's not connected.

My PC specs:
Modules enabled: None!
Extra info: I just launched Terasology and I got this, it could be an issue with the RX GPUs.
Most helpful comment
Another case. I am not able to open my inventory either, might be connected. I was trying to place water down to replace this issue.

EDIT: as pointed out by Cervator, there's no water if you run no modules, so it's not connected.
My PC specs:
Modules enabled: None!
Extra info: I just launched Terasology and I got this, it could be an issue with the RX GPUs.