sdlxliff files sequential numbering changes

sdlxliff files sequential numbering changes - Has it ever happened to anyone else before? I have 7 files, each containing several segments. I opened them all together, which of course temprarily "merged" them in one big file. I worked on them, and then closed them. After that, if I re-open each file individually, the strings do not start from "1". Only the 1st file does, the rest start with the number next of the last number of the previous file. For example, file 1 has strings 1-30, file 2 has strings that start from 31-50, and so on. Has this always been a feature and am I just noticing?