add project issue

reported by @nils.christian

When I import a model (PD_170202_2_fixed.zip, a version I once fixed myself), unselecting Root model in the Add project window requires me to click multiple times, see attached video. Not shown in the video is that the checkboxes need to be checked and unchecked multiple times in order not to encounter an error of multiple root nodes. I remember that I had the same problems with the old version.