Preambule: Dutch LibreOffice (32-bits?) installment on Dutch Windows 8.1 system, Intel 64-bits. Just a normal installation on a standard Windows version (Dutch) with all other application programs closed.

Earlier versions of LibreOffice, at least 4.2.5:
In the Installation wizard: unchecked (something like): leave the file linkings to Microsoft Office alone. So, the LibreOffice installer was not allowed to touch the file linkings of Microsoft Office documents!
Expected result: after installing LibreOffice all my MS Office documents should be linked to MS Word, MS Excel and MS PowerPoint respectively.
Result after installing: all Microsoft Office documents were linked to LibreOffice.
Remedy: opening all MS Office documents types once with the MS Office module in question. This changed the file linkings from LibreOffice to MS Office.

LibreOffice 4.3.0 screwed up linkings big time.
All documents linkings between Microsoft Office documents and Microsoft Office programs seemed to be intact.
However, double clicking on a Microsoft Office document or clicking on one of my Microsoft Office icons in the taskbar started not the Microsoft Office module as expected, but started some "Windows Installer".
I have no idea which installer, I cancelled immediately.
Again: the LibreOffice installer should have left all linkings to Microsoft documents alone, as instructed in the installer!
I found out a remedy: run the program Microsoft Office Diagnostics (NL: Microsoft Office Diagnostische gegevens). Luckily (the coupling to) this program wasn't screwed up. Somehow the MS Office Diagnostics program found out about the screwed up linkings and restrored them to the correct linkings.  There was no need to install something or another.

Please change the behavior in the LibreOffice installer. Leave all file linkings to Microsoft Office alone if you promise the user that these linkings will not be touched!