3188: "Make Screen Shot" fails if "Show Live Screen Shot in Dock" is unchecked

Parallels Desktop for Mac Build 3188: If "Show Live Screen Shot in Dock" is unchecked in Preferences, "Make Screen Shot" gives a black .png file. They obviously shouldn't be tied together that way, but at least the workaround is to check "Show Live Screen Shot in Dock" (I've got everything unnecessarily resource-using turned off, trying to diagnose intermittent freezes with 3188).