A Simple Puzzle

My original version of the histogram-generating code that I whipped up for the previous episode of FAIC contained a subtle bug. Can you spot it without going back and reading the corrected code?

private static int[] CreateHistogram(IEnumerable<double> data, int buckets, double min, double max)
int[] results = new int[buckets];
double multiplier = buckets / (max - min);
foreach (double datum in data)
int index = (int) ((datum - min) * multiplier);
if (0 <= index && index < buckets)
results[index] += 1;
return results;

Note that of course if this were production code, instead of demo code I whipped up in five minutes, it would be a lot more robust in its error detection; the bug that I am looking for is a bona fide error in the logic of the method, rather than things like "the method does not verify that min is smaller than max", and so on.

A hint: the first time I ran this code and displayed the results, the generated histogram looked fine. Then I made a small change to the arguments and the resulting histogram image was obviously wrong. Can you spot the defect?