This code looks bad (in org.knime.base.node.viz.plotter.basic.BasicPlotter.interpolateLine(BasicDrawingElement, boolean, boolean)):
double x1 = ((DoubleCell)domainValues.get(i).getX())
.getDoubleValue();
double y1 = ((DoubleCell)domainValues.get(i).getY())
.getDoubleValue();
double x2 = ((DoubleCell)domainValues.get(i + 1).getX())
.getDoubleValue();
double y2 = ((DoubleCell)domainValues.get(i + 1).getY())
.getDoubleValue();
The casts should be to DoubleValues. (This causes problems in some views, like the Hierarchical Clustering node's Distance view's changing the mapping method on any axis.)