umenu greys out foldernames in brackets

i'm populating subfolders into a umenu. now i came across foldernames which
start and end with a bracket e. g.
(1993) Wu-Tang Clan - Enter The Wu-Tang (36 Chambers)
umenu greys out that entrys and it's not possible to select them (disabled but still in the list)
why is that and how can i stop that behaviour? (without renaming folders) i'm so fed up with this kind
of suprises in max. grrmph