Save starts focused on a minecart partway down a short 2x2 spiral ramp with a locked door at the top and a lot of angry animals, plus one dwarf who has been pushing the cart up and down constantly. The dwarf has just found the cart 'inaccessible' while guiding it, possibly upon collision with one of the animals. The cart is apparently only balanced precariously, as it has rolled the rest of the way down at least once shortly after loading.

If the door is unlocked and the animals released, the dwarf will continue moving the cart, and has at least once found it 'inaccessible' with no other creatures present.

Relevant to bug report: http://www.bay12games.com/dwarves/mantisbt/view.php?id=7976