The default value set in FOPropertyMapping for the column-gap property is 0.25in (18pt), whereas the XSL-FO Reference prescribes a default value of 12pt. While fixing this bug is easy, it may break a looot of user documents that rely on the default value of column-gap. Releasing a major version of FOP would probably be an opportunity to fix it, if other backwards-incompatible changes are to be expected anyway. Leaving this as a reminder meanwhile.
resetting P2 open bugs to P3 pending further review