I had a somewhat similar experience some time ago, although not nearly on the scale of your own misadventure. ESC being more "Pause" than "Abort", or at least abort only after some part of the cached operation had completed, perhaps with the ambition to leave the system in a defined stable state.

At that point I concluded that any ZTree mirroring / syncing operation involving the deletion or overwriting of files without confirmation was too dangerous for me, at least with my modest level of ZTree comprehension, albeit going back to XTree in about 1985. (Somewhat off-topic, I rather liked XTree Win, although it was generally excoriated by its reviewers, both then and since.)

ZTree may be queuing up the deletes until last, for in case of power failure, lockup, crash. I wouldn't know. But synchronization with deletion is not for me except on the smallest scale, same as for drag 'n drop. Not for me absent either a rollback feature or sequestration of deleted / overwritten files in a separate location, for separate handling after review.