Hello,
I wonder why Libreoffice 3.5.0 can’t update to 3.5.1 automatically and asks me to download 3.5.1 install manually
LibreOffice does not support partial updates. Since it is built as a single application with several “modules”, you need to download the full package which is not a trivial download (nearly 200Mb for the Windows version).
Therefore since downloading such volume of data is not possible for many users (remember that LibreOffice is used in many countries and regions where Internet access is still limited to 56kbit/s analog modems) the program simply warns you that an update is available.