The GID for nogroup in /etc/group is -2. It is the first line in /etc/group. To my knowledge this is non-standard. It causes application breakage. The kernel(?) reports GID -2 in its 32-bit unsigned integer form (4294967294). ProFTPD truncates this to 42949 and chokes. The default GID for nogroup should be changed to something sane such as 65534 or 65535. Thanks.
Already fixed on CVS.