you save an illustrator file and then right away save the file as a PDF. if the illustrator file was not done saving, it saves the PDF with latest revisions, but the illustrator file, next time you open it, will be back to the last saved version. because we all work maddeningly fast, often one doesnt notice at the very top… "Saving 52%" in small type. wish, there was a warning, like your file is not done saving or are you sure you want to do this, like all the other million messages we get. Cannot tell you how many times I have lost work, not only that, it’s more like what the heck happened, I KNOW I made those last changes, were are they... I am not the only one that is complaining about this, discussed this with peers. Also, this wasn’t always an issue. Took me a while to even figure out what happened/happens.