Keyboard input "sticking"

On two separate computers I am having an issue where my keyboard input will appear to "stick". For example, if I press "W" to walk forward, and then let go, my character will continue walking forward until I press "W" again. This happens with every single keyboard control (sneak, jump, etc.). I have had this problem on every computer I have tried with a separate physical keyboard. I do not have this issue on my laptop.

One computer is running Windows 8.1, the other is running Windows 7 Professional.
One computer has a wireless Logitech keyboard, the other has a wired Dell keyboard.
Neither keyboard is dirty – keys are not actually "sticky".
Does not occur in ANY other program.
No mods installed on either machine.