5th Level Items = No Menublock

I've got my menublock setup to start at the second level, following the active menu item, and they aren't limited to a depth. I have a certain content type that's never in menus, but is using menu_position.module to assign it (via the content type) to a menu item 5 levels deep in the menu.

Everything else with this setup seems to work fine...but as soon as I hit the a 5th level page (assigned to a 4th level menu item), I dont get a menu block visible. If I assign the same rule one level higher (level 4) the menu block appears.

What else could be limiting this? I have 2 unused menu blocks that start at the 3rd and 4th levels...can other menu blocks interfere with each other's settings? (I tried deleting them but they appeared to make no difference).