Mystery solved. It would appear that the man page is slightly ahead of
abcde's capabilities. According to the upstream changelog, CD backup to
a single flac file was implemented in 2.3.99.3. Current version in
dapper is only 2.3.99.2, yet the man page describes this feature. I have
installed 2.3.99.5 from sid and this feature works as described.
Mystery solved. It would appear that the man page is slightly ahead of
abcde's capabilities. According to the upstream changelog, CD backup to
a single flac file was implemented in 2.3.99.3. Current version in
dapper is only 2.3.99.2, yet the man page describes this feature. I have
installed 2.3.99.5 from sid and this feature works as described.