Just a note that pressing ⌥⏎ inside the tags field allows to create multi-line tags.
I don’t know whether this is a bug or a feature. Glyphs continues to work fine and stores multi-line tags correctly.
The HIG highlights the possibility of adding the carriage return to the default tokenizing set, indicating that this is a common issue of using token fields:
Expand the list of characters that invokes tokenization if it makes sense in your app. By default, entered text becomes tokenized whenever the user types a comma. You can specify additional characters, such as carriage return, that should also trigger this action.