IlliniJeeper

You have to buy Minecraft in order to be able to play Technic/Tekkit.

Yes.

It's a bug that sticks Alt down when you alt-tab out of Minecraft. One of the mods makes Alt+click drop the stack of what you clicked. I can't remember how to completely eliminate the problem, but hitting escape instead of alt-tabbing to avoid it or hitting alt to reset the bug are two ways of working around it. Maybe it's in the keybind menu?