Yeah, thanks. Apparently, MCE::Map::import pre-assigns 'auto' to the CHUNK_SIZE property of a global, and if it's not assigned, then because of line 235, just before 'run', the chunk size is returned/gets undefined (why?) and somehow silently treated as zero (just guessing, didn't debug further), hence infinite loop. I'm now inclined to using the MCE proper anyway, but I think the situation is worth for Mario to have a look at.