Problem reading an output selection file generated by SWIFT

If I generate a file with ./swift -o fields.yml and then use it to select outputs I get an error message from the YAML parser. Something like:

Invalid line:229 '  VelocityDivergenceTimeDifferentials_Gas: 1', standalone parameter defined with incorrect indentation.

probably because the entry just before that had too long a comment.

The description field in the i/o is longer than what the parser can accept. Whether this is the problem or not I don't know.