We've been mapping '.' to '' in afw::table I/O, which unnecessarily complicates lots of things. We'd like to switch to using '' in the field names themselves, which requires ending this mapping in I/O, but we need to be backwards compatible. So we'll add a version to the FITS headers, and continue the mapping if the version is not present or is less than some value.
Until we do this, the new field names being used in meas_base won't round-trip.