A bug in the smurf:skyloop command has recently been found and fixed. This bug could cause negative or zero values to be included in the extinction (“EXT”) model. This in turn could cause effectively random behaviour in the other models, resulting in very poor convergence and some spurious values being introduced into the final map (if convergence does eventually happen). This bug is triggered by one or more observations having some time slices for which no extinction values are available (indicated by the presence of the string ” EXT:” in the skyloop log file). If such holes in the extinction data extend over only a few time slices, skyloop interpolates across them using the extinction values on either side of the hole. However, there was an error in this interpolation that led to the holes being filled with negative or zero values. This bug has now been fixed (as of 22nd May 2019). This fix affects both direct use of skyloop and indirect use via the pol2map command.