The mystery of the missing chevron.

Google recently released some ICS UI stencils for app designers. The image in the Verge story got me intrigued.

Screen_shot_2012-03-01_at_7

What is that inverted chevron symbol on the left of the navigation bar where the back button normally is? I have a GSM Galaxy Nexus and have never seen it, but a couple of comments under the story say it is displayed whenever the multi-tasking menu or keyboard is visible. What's going on? Is this something that other ICS users are familar with? If so, why does my phone never show anything other than the normal "U-turn" back arrow?

OK, this isn't exactly a mystery worthy of Sherlock Holmes, but it has got me curious. I'm sure a knowledgeable bunch like you have an explanation.