Blocks are spontaneuously placed and cannot be stopped

Whenever I place blocks, sometimes it spams that block I placed even though I didn't click for that long to place them. It's really frustrating and has been happening since 1.6.2 Pre-Release and is still happening even in 1.6.2 Release.
The only way I can stop the auto spamming of blocks is if I press Esc. It's really infuriating that I can't just place blocks without hassle.