A77 AF disables itself with Tamron AF 90mm f/2.8 Di SP A/M 1:1 Macro

I'm getting strange behavior with my A77 and the Tam 90mm macro. I really enjoyed this lens on my NEX-7, but when using it on the A77, it'll sometimes hunt for focus until the lens is at the top range (extended all the way) and I'll hear a little click in the camera. At this point AF will not work. Switch the camera off/on sometimes doesn't fix it and I need to dismount/mount the lens for the camera to recognize the lens again. What's going on here?

Another thing I noticed with this lens: maybe this is normal but the AF effectively locks the focus ring of the lens when in AF mode. When I switch AF off, the focus ring turns freely. Whereas with the Minolta AF lenses I have, it doesn't lock the ring like this. Is this the difference between focus "by wire" and other AF means?

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1500 years ago, everybody knew that the Earth was the center of the universe. 500 years ago, everybody knew that the Earth was flat. And 15 minutes ago, you knew that people were alone on this planet. Imagine what you'll know tomorrow. -MIB