Is it possible to go into a bit more detail about how exactly you are doing these things? Maybe a screenshot or two? The only thing that I can think of is perhaps OF is trying to adjust the display parameters so that the item you moved remains visible (which might then cause many other previously hidden items to appear).
You can change the context of an item (in a context mode view) a number of ways, including:
- select item(s), bring up inspector, change context setting
- right- or control-click on selected item, set context from pop-up menu
- drag item to a different context in the sidebar
- enter or select new context in context field, if showing context column in view