Currently, Histograms have an array of sampleValues and Bins, which have counts and DiagnosticMaps. addSample() always increments the bin count, but may add the sample value to sampleValues, and may add the diagnostics to the bin's diagnostic maps, but there's no connection between sampleValues and diagnostic maps. When a bin is brushed in histogram-span, its DiagnosticMaps are displayed, but histogram-span should display the specific sample value that originally went with each DiagnosticMap. This is an architectural bug that arose due to the history of adding sampleValues and bin diagnostic maps independently.