Butterfingers (I keep dropping stuff!)

[Moridin]

Title: Butterfingers (I keep dropping stuff!)

Version: 3.1.3

OS: Windows 7

Java Version: Version 7 Update 9

Description of Problem:

It started when I would have people on my server. Occasionally, I would try to click on an item to move to my hotbar, and they would fly out as if I had tossed them. This wasn't too big of an issue at first, because it would always stop after a little while. Now, though, its starting to happen even when I first log on with no one else on. Please, if there is ANY way to fix this, please, please let me know. Its driving me crazy!

Error Messages:

Error Log:

[Niavmai]

Your alt key is stuck. Or maybe it's shift. One of those. Just press it once in game, and it should unstick.

[Moridin]

Thank you. I've been looking for an answer to this for a while and none of the other things people had told me worked. Glad to finally know what's happening