When using the mouse on an item in a Scene2D then if you press and then move the mouse outside of the item it will act as if it is still pressed even if it is released.

This can be reproduced with the scene2d example by doing the following:

• Middle click to stop the rotation
• Press and drag one of the sliders until you leave the item
• Release the button
• Move the mouse back over the item and it will move the slider handle still