The get_unicode_or_ascii_string() routine, used in several places in the SMB and SMB2/SMB3 dissectors and in some other places, doesn't just fetch UTF-16 when fetching a Unicode string - it turns everything that doesn't look like a character from ISO 8859-1 into a question mark.
So, yes, please file a bug, with a sample capture; we definitely need to fix or replace get_unicode_or_ascii_string() and, having done that, we may also need to change the display format for the fields mentioned in the other answer.