It is WAY too easy to accidentally click and do some piece of damage that you can't even tell what you did. Then when you do finally discover it later, you learn it's not reversible. Not cool.

Somehow I managed, with a single brief movement of my mouse across some listing of data, to change a task to a list. No.

PLEASE, either give a failsafe, "Are you sure?" screen, or make it evident somewhere what just happened. And then make it reversible.