Ok, I'm not sure if you are aware of what I mean by Double-Input Lag. Basically, I right click once, a millisecond of lag, and it places 2-3 blocks. This happens the same when breaking a block. To note: It only happens it certain areas.

These forum posts should help you understand:

http://www.minecraftforum.net/topic/100811-one-click-places-two-blocks/
http://www.minecraftforum.net/topic/1429414-double-block-placement-bug/
http://www.minecraftforum.net/topic/867046-help-100-placing-2-blocks-at-a-time-bug/
http://www.minecraftforum.net/topic/828917-how-to-fix-double-block-single-click-issue/
http://www.minecraftforum.net/topic/818450-place-a-block-twice/

The list goes on. I can provide video footage if it helps. It only happens in certain places, I'm putting my money on some kind of light-rendering bug. Perhaps a lag in the last tick of placing a block meaning the click carry's on, forcing another blocks to be placed.

Thanks a lot,
Serilex