It seems that the opportunity to undo the previous action is only available briefly, while the "undo" pop-up is visible. It would be helpful to be able to undo previous actions using some on-screen button. Users may also be accustomed to using Ctrl + Z to undo previous actions.
Say that you highlight all the tasks in a list, and move them to another list.
There is no way to undo this action currently. It would be great to add the capability to undo most 'mass' actions (where you select a whole bunch of tasks and perform an action on all of them like changing their status or moving them).