\documentclass{article}
\usepackage{fontspec}
\setmainfont{DejaVu Serif}
\setsansfont{DejaVu Sans}
\setmonofont{DejaVu Sans Mono}
\begin{document}
Hello World!
\textsf{Hello World!}
\texttt{Hello World!}
\end{document}
compiled with XeLaTeX gives me this:

Copying the output with SumatraPDF even shows regular space characters between the letters and a line break between the words:
Hello World!
Hello World!
H e l l o
W o r l d !
(Copying it with Adobe Reader XI Win, however, yields three identical lines.)
This problem doesn't occur with LuaLaTeX:

The OCR-layer-text for LuaLaTeX is flawless as well, using either PDF viewer.
I assume this is a XeTeX bug? Can I circumvent it somehow?
I'm using MiKTeX 2.9, and version 2.33 of the DejaVu fonts, which I think came preinstalled with Windows (7), at least I can't recall manually installing these fonts. This version seems to be the current version, at any rate.
P.S.: If someone can recommend another monospaced font for code that a) goes well with Linux Libertine and b) contains lowercase Greek letters, that'd be helpful, too. But that just as an aside :).
\setmainfont{Linux Libertine O}uses pfb files instead of otf/ -- every MiKTeX user with thedejavupackage installed should get that behavior. I'm kinda busy right now, but I'll post some more details towards the weekend. – doncherry Nov 29 '12 at 00:54dejavuinstalled in MiKTeX with both the Truetype and Type1 font files and I have the fonts inC:\Windows\Fonts. But I don’t get this behaviour, what is confirmed by several users! BTW I can’t tell from the log file, which font files are used without one fact: It’s only Truetype. – Speravir Nov 29 '12 at 04:56DejaVuSansMono.ttffromC:\Windows\Fonts? (In order to do this, I usually have tomovethe file somewhere else withcmdrun as admin.) Have you ever changed anything in yourlocalfonts2.conf(or related files)? – doncherry Nov 29 '12 at 05:10localfonts.conf. Here on my computer the Windows fonts folder is read in first, then the Type1 fonts folders (first local, then MiKTeX’ own), after that the MiKTeX opentype folder, and last of all the MiKTeX truetype folder! – Speravir Nov 29 '12 at 18:50localfonts2.conf. But perhaps I need to delete some font cache first? – Speravir Nov 29 '12 at 19:14