When I close one layer, others open

[jotasprout]

For example, if I click the collapse thingy for +Left Arm copy in Figure 1 in the image below, it collapses that layer but also expands the +Left Quarter > Head layer(s).

I've never seen this before and it's at least the second-most irritating thing I've ever seen Illustrator do. 

How do I make it stop?