Fix exception when dropping an item from another document on the selected category group.  It's not clear why this no longer worked.
Fix exception when dropping an item from another document on the selected category group.  It's not clear why this no longer worked.
WoLpH/skim,WoLpH/skim,WoLpH/skim,WoLpH/skim,WoLpH/skim,ycaihua/skim-app,ycaihua/skim-app,ycaihua/skim-app,ycaihua/skim-app,ycaihua/skim-app