A WBS shows a work package called Window Sill Flashing as a child task of Exterior Masonry and Windows. Both parent work packages are at the same immediately preceding level in the WBS. The masonry contractor claims that window sill flashing is the responsibility of the windows installer, and the windows subcontractor claims that the masonry contractor should perform this work package. Neither of the respective contracts specifies who should be responsible for the work. What was wrong with the WBS leading to this dispute?