I have an action group that translates defined by me substitues of illegal characters into illegal characters. Also I have defined them in my "Tag - Filename" icon. I use them to copy the name of the song from FILENAME to TAG title and from TITLE to FILENAME
All of my my "translations" work as they should. With one exception:
TITLE >>> FILENAME
Æ >>> Ae
æ >>> ae
FILENAME >>> TITLE
Ae >>> Æ
ae >>> Æ
So it seems, there is a bug that makes lover "ae" into upper "Æ" [instead of lower "ae"], when coping from FILENAME to TITLE
[un-checking the "case sensitive comparison" did not help]