Hai, Even its long time after the initial report. You might be right. this "old" bug recently got updated. https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=581199 (snap) Idmap looks for the first occurrence of and @ sign in the name string and assumes that the @ sign is the one of user@virtual_domain rather than using the one of username@idmap_domain (user@virtual_domain@idmap_domain).
As a result, the UIDs / GIDs cannot be resolved and the ownerships are reported as 'nobody'. Best regards, Louis
