I had trouble tracking down an error in javascript, and it came from get_itemIndexHierarchical (and _itemIndexHierarchical) returning string values rather than number values, such as "12" rather than the expected value of 12. This appears to be a bug since the row index should always be numeric.
I got around it for this particular issue, but I'm concerned it may pop up in other code. Would you agree this is a bug and something you can change?