When working in the image editor, rotate and flip actions are immediate actions, where you see the result and you always have the "Cancel editing" button at hand.
The cropping on the other hand opens a new view, where you have a new action to actually do the cropping, but a action to cancel it is missing.
I was not sure how to get back to the other "view" and get rid of the cropping, so first I closed the whole tab, after fiddling around.
IMHO there should be a "cancel crop" together with "crop image".