I'm useless with Mantis, so I cannot report it there. I embark with an all-miners-bar-one-lumberjack embark and start setting up a fort to use in future. This meant moats and fortifications of every type, a sort of small megaproject. I dig a moat that ends in a waterfall (The moat feeds off a river coming into my map).The Liaison and caravan arrives. The caravan decides to swim through 5/7 water despite the still-dry land south of it. It loses all the stuff which gets pushed over the waterfall. A miner of mine drowned in the thing along with all the merchants and wagons and wagon pullers. The liaison refuses to leave the fort, hanging around in a tavern instead after doing the trade agreement stuff. Then the river froze over and the animals which were in the cages in the wagon died from icification, but showed up in the units list, even allowing me to (z)oom to location, which just showed ice walls.
TL;DR: Merchants path through 5/7 water despite having a clear path downstream, Liaison refuses to leave if the caravan is destroyed and caged animals that die from ice stay on the units screen as alive.
For the last one, still waiting to see if they can 'die' of starvation when already dead, as there was a few caged horses and llamas