Bug 965548 added a new exit edit mode button to a focused URL bar. On tap of the button, we dismiss the keyboard and drop focus to the URL bar. On device back button, we dismiss the keyboard. We retain showing the the new button and we drop focus to the URL bar. This seems to be a mixed state. On device back button, we should match the behaviour of simply using the newly added button. -- Nightly (04/22) LG Nexus 5 (Android 4.4.2)

I would say we actually do not want this. We added the "cancel" button to support users who wanted a way to leave the awesomebar and return back to the page they were on previously in a single tap. But we know there are also users that tap the back button just to hide the kayboard so they have more room to scroll content in the awesomebar. They don't want to leave in one tap, they want to free up space on screen.

I agree with Ian - this is intended behavior.