wobble() used a correction to the small angle rotation approximation, adding in the leading x_p yp correction term that was ommitted in the small-angle approximation. Since x_p and y_p are typically small (below 0.1 arcsec), the product is at the level of 10^-14 radians, or 0.01 μas level only. This correction was applied incorrectly when it was used in the reverse direction (PEF/TIRS -> ITRS). While it is not a measurable error, it is nevertheless noticeable at the numerical level, hence we will correct it in 1.4.