I have installed LibreOffice on my harddrive at C:\Portable\PortableApps from the PortableApps start menu, so everything should be standard setup. When I try to start LibreOffice, either from the PortableApps launcher or by double-clicking the LibreOfficePortable.exe directly it often fails to launch a user interface window. When it fails I have to use the taskmanager to manually kill any LibreOfficePortable tasks (there is always at least one) and then it usually works.
This is happening on a brand new Windows 8 64-bit laptop system built by Lenovo. Other PortableApps launch just fine.