This seems like an Integer overflow problem. Trying to put a 64bit integer into a 32bit integer, or it is an unsigned int being placed into a signed int (but that seems less likely) or similar.
This is a bug. You should file a PMR with IBM on this. Include a link to the this forum post in the PMR as well as other details. Then open an RFE with a reference to that PMR as well as a link to this forum post. Then let me go bug some developers directly to open an actual bug. See here: How to ask for IBM product help: PMRs, RFEs, and more
CC: @AlanM