PSD is not my favourite file format (2009)
> Why, for instance, did it suddenly decide that these particular chunks should be aligned to four bytes, and that this alignement (sic) should not be included in the size?Not saying this happened here, but I have seen this type of mistake before. It was because they "simply" cast a C/C++ struct to a binary blob https://en.wikipedia.org/wiki/Data_structure_alignment#Typic... and wrote that to disk (or sent over the network in my case). So that particular compiler version and architecture-specific struct field alignment became the "official" format.  It just takes one goofy mistake like that and everyone has to deal with it for years to come.