This is a feature. To save you time from transferring something that would eventually fail, it checks for the available space on the destination and if there isn't enough space, it will stop tha process.
some FTP server just accepts the file even though it fails to write them, then issues a success code. That, to me, is even worse.
Are you sure this isn't a bug? Is the bug fixed where the free space on the remote machine is wronly indicated? Cause I remember trying to transfer some files and failing due to this issue, while the remote machine had plenty of room.