Collaborator is configured such that once any defect has been found in any file of a review, then no files in that review can be removed. Your only option is to delete the review and make a new rev...
In our case, many of the files we review are not code files from a change list, but individual spec files or something. If I have added a file by mistake (or the wrong version from my computer), I can't delete the file unless I delete the whole changelist (which is not really a change list like multiple code files). I don't want to do that because of the valuable information there. I just want to remove the file that was mistakenly added. Even if I have not made a comment to it, but have made a comment to another file in the list, I can't remove this bad one because the tool thinks it is part of a list and can only delete the entire list! There needs to be a way to differentiate between a list of nested files and individual files.