The only known bug occurs with the container elements. That is, those that refer to other elements. For example, the Distance element in the submodule Linear kinematics of particles. If this item is added into a problem, but not assigned any mobile or point, wanting to get the answer FísicaLab not show anything, and stay Solve button pressed. With a click on the Delete all button, Solve button return to its normal state. But of course, deletes all elements of the problem. To avoid this, do not add container elements if not used.