XI mapping function SUM calculate wrong?

Hi, I suspect the default SUM function in XI IB to calculate wrong on big decimal values. I tried the user defined function described at the bottom of this thread: ?sap-gui-'sapdp00'-error

But I miss out something. It does not SUM for the whole document, as the default SUM function would do.

Any ideas?

Would any service packs correct this? Anyone else with this problem? Is it a bug?