Hi Johan,
You have run into an issue with markdown syntax. When I tested RTF001_#_1/67_# in the Identifier field, it displayed as RTF001_#1/67#.
As a short term solution you can turn off markdown at Admin > Settings > Markdown. If you do that, don't forget to rebuild your search engine once you have saved the change:
best of luck!
Corinne
Systems Archivist
Artefactual Systems