I'm playing the X-Chronicles mod but I believe it's a bug with the game rather than the mod.
I've fired an explosive grenade from the grenade launcher and it went off the map and now the unit's turn won't end.
To reproduce though get a grenade launcher, fire explosive rounds at an enemy next to the map edge until it misses off the map.
Edit- I couldn't access the options menu to close the game properly so I alt-f4ed it and ran it up again, the ironman had saved it from just when I fired the round but I could select other soliders again so I finished the turn, which was fine, the aliens had their turn, which was fine, I continued with my next turn which was fine until I tried to move the solider who had fired the grenade round. As soon as I tried to move him he didn't do anything but his turn won't end again and I can't access the options again.
In the attached save just try to move the solider which starts selected.