Robocopy mir deletes files when network goes down?

Question

I've inheritted some server backups and I heard from the person that if the network goes down while robocopy is running it will wipe all the destination folder if /mir is used. He said it is because there is some cache going on and robocopy just sees the directory as blank.Is this true? I thought robocopy builds a file list first before it start processing the information. If it can't access the files then it will either retry or skip them.