Using the LibreOffice_4.2.3_Win_x86.msi, it seems the installer breaks Microsoft Office association. On Windows 2008 (Office 2010), using a custom installation with “checkbox unchecked for Microsoft Office association” it works fine. But on Windows 2012 (both Office 2010/Office 2013), it seems to remove the file association from Office. Any advice on why this is happening or completely removing file extension association? I tried the MSIEXEC parameter with the REGISTER_NO_MSO_TYPES too, and it didn’t help.
This looks like a bug. Can you please report it at bug tracker: https://www.libreoffice.org/get-help/bug/