#314 tier layout bug, non-overlap feats are overlapping

[Brian O.]

Obscure tier layout bug (reported by Suzi):
It can detect overlaps in sequence space, but is not detecting overlaps in draw space. This means non-overlapping features on the sequence, that do overlap when drawn are still colliding. It only happens for features that are drawn outside their own limits. Like labels (they have a special check) or the P element triangles that have a forced minimum width.