Change Assert(Ptp.t_data->t_xmax == tp.t_data->t_xmin) to :

Change Assert(Ptp.t_data->t_xmax == tp.t_data->t_xmin) to :
/*
 * Read above about cases when !ItemIdIsUsed(Citemid)
 * (child item is removed)... Due to the fact that
 * at the moment we don't remove unuseful part of
 * update-chain, it's possible to get too old
 * parent row here. Like as in the case which
 * caused this problem, we stop shrinking here.
 * I could try to find real parent row but want
 * not to do it because of real solution will
 * be implemented anyway, latter, and we are too
 * close to 6.5 release.        - vadim 06/11/99
 */
if (Ptp.t_data->t_xmax != tp.t_data->t_xmin)
...