Only (re-)draw residues with multiple features once to improve performance and SVG/EPS export

Whilst looking at the SVG output for JAL-4603 (not related to this issue) I noticed that residues with features are drawn more than once, layered from bottom up. The first layer is the plain residue (with colour background if colouring is turned on), but for every feature that residue is in, a background colour box (for the feature) is drawn with the residue letter then drawn on top. This happens for every feature with each one hiding the previous one(s).
Whilst this works in practice, for the SVG/EPS output it results in unnecessary items in the SVG file. I also wonder whether there is a performance hit for MSAs with lots of features when scrolling.
I haven't looked at the logic for feature colouring yet but it might be possible to optimise to only draw the upper feature (perhaps draw from top down with a skip for residues that have already been drawn)?