IB bind to path with dots

I have a textfield I am binding to user defaults in IB. It works when the Model Key Path is a simple key "highscore" and defaults has a string in "highscore", however if I put a dictionary with a "name" into defaults instead, the binding "highscore.name" to the text field won't work.

I can nslog [defaults valueForkeyPath"highscore.name"] anywhere in code and see the expected output.

 

Okay, I found that if I bind manually with code in awakeFromNib, it works as expected, however I am still curious why it didn't work before, is this a bug in IB?