I tested with the latest node version. Tried to download a file that was uploaded with "TargetFilename=" (^=empty), and used key "CHK at bla/filename.ext" for the download. Surprisingly the node did not return error code=11 to indicate I should retry the download without a filename, but the node did download the file.
Is this now transparent for an application and you forget to tell us about? Should an application still check for errorcode=11 and remove the filename from a CHK key?
