When using the Roll action of a smoke grenade to a position shown in the screenshot, an error occurs: "Can't perform action - impossible throw!".

Well I didn't think it was that impossible so I decided to give it a server-side try anyway. The grenade disappeared from my inventory and TUs were spent as if it was thrown, however it doesn't seem it went anywhere. If there was indeed an error, I'd expect the grenade to remain in the inventory.

Also not sure what that piece of smoke in the upper-left side of the screen is doing there - I never attempted to throw anything in that direction.

This seems to happen all the time.