I have to correct myself: As it turns out, this does not seem to be a urzagatherer issue, but a telegram issue. Apparently telegram does somehow cache files and instead of downloading the new file just copies the old file, despite showing the correct file size from the new file...
This makes no sense at all, but is not your problem :P
sorry for the inconvenience (maybe it will at least help someone with the same problem in the future)