Metadata assignment in document object

Hello everyone! Did anyone encounter weird behavior from metadata assignment in Document object?

I am trying to pass 'appendix' key and a string value, which is a string of paths with a '';'' separator, but for some reason it does not work. For example I am essentially trying to do this:

'appendix': '\folder1\file1; \folder1\file2; \folder1\file3'

I did print out those strings and they do properly display.