Not what I was doing. I control click individual files to add/remove them from the selection. Removing does not work correctly (the file tends to stay selected) and adding also does not work correctly (it's inconsistent, but about 1/3 of the time the file is added to the selection and about 2/3 of the time the file becomes the selection, i.e. everything else is deselected). This behavior is inconsistent with every other gui app with multi-select listboxes I use, and the behavior is even inconsistent over time, since control click adding DOES work correctly SOME times...