We wanted a group consisting of user A and user B, both of which are members of a group that has read/write privileges so either of those users and upload, delete, download files from a given directory.
Having got the acviccap account with subfolders set up on nfs.hcmc.uvic.ca I did some testing (with help of Martin and BS of CCAP/ACVI) specifically on group permissions.
BS used Cyberduck and I got a copy and confirmed results. I tried Filezilla and my copy of Transmit and they also had a similar problem:
If client is set to not impose permissions on server, we expected the files and folders on the server to get the group settings read/write. The FTP client default behaviour did result in directories have acceptable settings, but files don't have group write; it's possible to set the upload configurations in the FTP client to force acceptable settings (namely 775 for folders and 664 for files), but it's one more thing and affects all uploads executed by the client (i.e. scope is not limited to a given connection).