It is annoying that it's easy to tigger a popup while attempting to travel your mouse to another popup. But the option to have to click to close the popup may become a chore if a mouseover is still used to open the popup in the first place. A click to open and click to close would be a great option. It would still seem like a chore but some themes would almost require it since the horizontal space between popup items is so small.

Having the popup appear at the location of the mouse would also be a good option since you wouldn't have to travel the mouse along a thin horizontal path to get to it.

Another option might be to have only the area around the menu arrow activate the popup with a mouse over. It's a smaller area to aim for but creates a dicipline of always having the mouse beside where the popup will appear. Of course you could train yourself to do this without forcing it through popup anyway.