Because the way I modified the diff-generator in !9 (merged), turns out it confuses the parent dir walker that creates the parent dir entries in the diff image, resulting in the image that looks like before !8 (merged) is merged (files in subdirs without entries for parent dirs). It's not a big issue in itself (tests show that the added dirs doesn't affects the extraction due to Busybox limitation), but it's probably still worth fixing...