Clicking the "Crop Image" button in the Image editor does change the bottom buttons to "Cancel" and "Crop Image" but it does not always activate the image cropper widget.
Sometimes it is activated on the first click, sometimes 2nd, sometimes only after many.
Seems to a problem most on firefox (also with all addons disabled). Have also had problem on Safari. have not seen problem on Chrome.

For example have detected it on this image: /magnolia-bundled-webapp/.magnolia/admincentral#app:assets:detail;/demo-project/img/bk/Stage/abstract-tiles-red