I have 4 duplicates that aren´t duplicates, how do I let Mayan know this?
Without more context or access to the installation is hard to say what is this or what caused it. Seems the duplication detection was interrupted of the document file content updated after the document was created.
Try running the duplication scan again from the Tools menu. This will launch a background task that will compare all documents against each other. Since the duplication logic will run for each document, this will take a long time, which is why it is normally done only once at document creation as an optimization but the tool option was added for situations like this.
