Recently I've been using the SE Gaming Minecraft server a lot, and today when I tried to craft watermelons into seeds, I discovered that they wouldn't move to the crafting table when I clicked them, they moved to my quick-use bar, then moved back to my inventory when I clicked them again. I checked my Shift key, and it was not compressed, so that's not the problem. What is the problem?
I know you checked your shift key, but 1 explanation would be that you pressed shift multiple times resulting in an affect called sticky keys. One way to remove it is press shift repeatedly until your computer has a pop up message. Then you have to press cancel or something.
Sorry if this isn't specific enough.