Problem with plot in several cases, font issue?

Dear all,

I am having problem on plots in R for some cases.

For example:

plot( 1:10 )
text( 1:10, letters[1:10], cex = 1)

works well but :

plot(1:10)
text(1:10, letters[1:10], cex = 0.9)

returns :
Erreur dans text.default(1:10, letters[1:10], cex = 0.9) :
   impossible de charger la police X11
-adobe-helvetica-%s-%s-*-*-%d-*-*-*-*-*-*-*, de face 1 et de taille 11

(sorry for the french).
In this message, for other cases the function may changed (it can be
axis( ) for example) but it always a font problem.

I encountered this issue various times (with more complicated graphics).

I'm working on ubuntu 12.04 with R 3.0.1 (2013-05-16).


The capabilities function returns me:
   jpeg      png     tiff    tcltk      X11     aqua http/ftp sockets
TRUE     TRUE     TRUE     TRUE     TRUE    FALSE     TRUE     TRUE
  libxml     fifo   cledit    iconv      NLS  profmem    cairo
  TRUE     TRUE     TRUE     TRUE     TRUE    FALSE     TRUE


I think this may be an issue with my installation, but I could not
figured out what was the missing package.
I tried this on other computers. I did not see the same bug.


Thanks in advance for the help,

Alice