As illustrated in the bug report there are times when a complex arrangement of editors can result in invalid edges after a "tolerant join".
This is because it is only the edges of the two affected areas, plus those shared by immediate neighbors, that are adjusted to align correctly before merging. But there are times when there are disconnected editors that need to have their edges adjusted as well.
This patch fixes that perfectly. Before joining two areas vertically it aligns all screen verts that match the horizontal position of the source and target area. And for horizontal joins it does similar, aligning vertically any screen verts that match the two areas.