Can confirm - seen this in my test 40.01 fortress, but didn't tried to reproduce later. In my case there was crash also, not only FPS drop. But also slight difference in the reason - it was wild animal.
In my case, I managed to close raven, that tried to attak one of my animals (or dwarves?) in my 'bump area' - part of the coridor near main entrance with fortifications on the sides and doors (planned bridges, but...) to lock it down.
The moment raven tried to leave through the locked, non-pet passable door outside the fortress, FPS dropped from 100 to 8-12, and then dwarf fortress crashed.
It happened in the 1st year spring or summer, so I had no save and abandoned fortress.
Also, though, that this might be fixed in later releases with pathfinding bugs. What DF version do you use?