Just after the launch of Yohkoh, it was found that there was an error in the way the DP inserted BCS PH-data into the telemetry frame during medium bit-rate. This can be seen a ``hole'' that steadily marches through the data in successive spectral integrations; when viewing the light curve, a periodic, but structureless reduction in the count rate is seen in medium bit rate. When the hole is not in an interesting part of the spectrum, the data can be used, otherwise it should be rejected. The problem was corrected by a patch to the DP in late November 1991.