if you have a Key over a specific length (which is obligatory sometimes e.g. if you create an index on a text-column) the generateChangeLog-command does not export the length. It might be, that it is not even possible to save the length as a specific attribute because it seems not to be mentioned in the xsd.
CREATE TABLE test (id text,UNIQUE KEY (id(255)));
will generate a changeLog by the generateChangeLog-command like this: