I'm starting to suspect I broke my dwarves' brains somehow...
I'm finally back up to the "Dragon attack" (resulted in running straight into a cage trap because I removed ramps until creatures had to march in along just a couple predictable paths), and when the dragon hit, I once again hit "only soldiers go outside".
My dwarves pretty much dutifully once again hid themselves from harm.
Except for one character, who is my second-best cook. She was carrying a bag of rat weed seeds from the earlier tradesplosion. Her job was listed as "dump item". This was odd because she was sitting right at the enterance to my fort, doing nothing. I mean, sitting there watching the dragon walk by as it went and got itself stuck in a trap, doing nothing. When I let dwarves back outside, she immediately ran outside to just go toss the seeds onto the grass.
What's worse is that this stack of seeds had to have come from inside my fort, and I have NO outside dump sites, meaning she's sitting out in the open waiting for the green light to march out in the open when I have the "outside forbidden" to do something she's not even supposed to do. I have NO idea what my dwarves are thinking anymore, and I'm really starting to suspect that the large number of random trash items is starting to cause severe AI bugs.
edit: There were actually several pages of seeds sitting on a single tile in the grass near my enterance. Apparently, my farmers have been dumping seeds here ALL YEAR without my knowledge.