Why does fontspec change the maths accents (and only with lualatex)?

Question

In the minimal example that follows luatex doesn't place the accent correctly (it's too far left):

\documentclass{minimal} 
\usepackage{fontspec}
\setromanfont{Linux Libertine O}
\begin{document}
\(\bar E\)
\end{document}

But if I compile it with xelatex, or with lualatex and \setromanfont{Linux Libertine O} commented out, everything works fine.

I believed that fonspec was only for text, and not for math. So why this strange behaviour ?

Answer 1

This is what I get when calling \showlists after the formula:

LuaTeX

### horizontal mode entered at line 6
\whatsit
.\localinterlinepenalty=0
.\localbrokenpenalty=0
.\localleftbox=null
.\localrightbox=null
\hbox(0.0+0.0)x20.0, direction TLT
\mathon
\vbox(8.20554+0.0)x7.95831, direction TLT
.\hbox(5.67776+0.0)x0.0, direction TLT
..\OT1/cmr/m/n/10 ^^V
.\kern-4.30554
.\hbox(6.83331+0.0)x7.95831, direction TLT
..\OML/cmm/m/it/10 E
\mathoff

XeTeX

### horizontal mode entered at line 6
\hbox(0.0+0.0)x20.0
\mathon
\vbox(8.20554+0.0)x7.95831
.\hbox(5.67776+0.0)x0.0, shifted 2.31252
..\OT1/cmr/m/n/10 ^^V
.\kern-4.30554
.\hbox(6.83331+0.0)x7.95831
..\OML/cmm/m/it/10 E
\mathoff

There is clearly a problem with LuaTeX; it can be due to fontspec as, when not loading it or loading a different font than Linux Libertine O (I tested Old Standard and TeX Gyre Termes) I get the following:

LuaTeX (without Linux Libertine O)

### horizontal mode entered at line 6
\whatsit
.\localinterlinepenalty=0
.\localbrokenpenalty=0
.\localleftbox=null
.\localrightbox=null
\hbox(0.0+0.0)x20.0, direction TLT
\mathon
\vbox(8.20554+0.0)x7.95831, direction TLT
.\hbox(5.67776+0.0)x0.0, shifted 2.31252, direction TLT
..\OT1/cmr/m/n/10 ^^V
.\kern-4.30554
.\hbox(6.83331+0.0)x7.95831, direction TLT
..\OML/cmm/m/it/10 E
\mathoff