I made a couple of posts in Liquibase Users on this topic. For example: http://forum.liquibase.org/topic/mysql-types-don-t-match-when-generating-diff-logs
My observation is that the XML diff files use some kind of cross-platform format for data types but when applying them to MySQL it seems to convert to the correct type.
I’d like some kind of a confirmation from the developers that this is indeed the case.