The page title for individual question pages is formatted:
(tag) - (question title) - Android Enthusiasts
But only when the question has a single tag. I personally just like seeing the question title there, why do single-tagged questions show the tag first, and can and should we change this to be just the question title?
It's done for Search Engine Optimization, because question titles often don't explicitly mention the common names for their topics.
Sounds like you'd be interested in this question on the main Meta site: Should we stop adding the most popular tag to the HTML title on every SE site?
One instance where tags aren't added to the title, is if the tag is already included in the question title, eg Any Android phones that don't support Bluetooth? (random example from the current front page) where the title already includes the word "bluetooth" so there's no need to add the tag. This could be what you're seeing in the instances when the tag isn't added to the page's title, and it's just coincidence that most of those happen to only have one tag. Here's an example with more than one tag Connecting Android to Ford Sync via Bluetooth? where the tag isn't added, as it's mentioned in the question title.
