I've been looking into why the last point of the chart isn't plotted. It looks like two problems:
For Grouped data, the last group isn't being created. In seriesProto.processData = function() (line 12000), in the section starting: if (dataLength > maxPoints), the code inside while (groupPositions[1] !== UNDEFINED && processedXData >= groupPositions[1]) isn't called for the last set of values for pointX, high, low, open, close. This code needs to be called after the for loop exits to store the last groupedXData and groupedYData values.
For ungrouped data, it looks like cropStart is being calculated incorrectly. In processData: function() (around line 9610), I changed cropStart = mathMax(0, i - 1); to cropStart = mathMax(0, i); which seemed to fix the problem.
Regards,
Steve