Data before 'xxx' confused the scalar jyperk with the deprecated array jyperka antenna based array. In order to correct this data, such that programs like invert will correctly compute the noise characteristics of the resulting image, use the jyperk program:
jyperk vis=xxx.mir out=yyy.mir
One can optionally supply an array of Jy/K values for the 15 antennae, but the current values in the 65 and 145.3 for OVRO and BIMA antennas resp.
See also bugzilla bug # 339.