cant split stacks in the 1.4 update, or even in the 1.4 prerelease

Hello,
I recently updated the 1.4 pre-release and when I log into a server, or even my single player, I cant seem to split stacks of things which makes crafting impossible. I Recently updated the to the 1.4 when it released today. When i switch the button 1 to 2 and vice versa, it seems to split but makes it very hard to play. I cant seem to figure out what is going on with my Minecraft client. I have no idea why this is happening because i have never had this problem before, although this is my first time updating a pre-release. Please Help. Thanks.