I have a breakpoint that looks like this
If you debug your code on the device the parameters when you hit your breakpoint will consistently be in registers r0, r1, and r2. If you use
po $r0 you'll see the object receiving setSelected. If you use
po $r1 you'll get "no Objective-C description available" because that's the selector. Inspect $r2 to see if selected is being set to YES or NO. It's a similar story on i386, but I can't remember off hand which registers are used.