Giacomo Vianello pointed out a confusion in using extractor (actually extract in xselect) when multiple event files with differing WCS are read. The extracted image has sky coordinates corrected to the same WCS however the extracted event file does not. This means that doing a straight extract image produces a sensible looking image but doing an extract events followed by an extract image produces multiple sources. I've checked in a fix (as v4.68) which corrects this and transforms sky coordinates to the same WCS when extracting events. This is at a slight cost in speed but only for the case when WCS differ.
Keywords: HEAsoft, xselect, extractor