"Force pasting as plain text" not working

Hello,

I'm using the ckeditor for a long time now, and always used the "Force pasting as plain text" option.

But in my latest project, this option doesn't work.
If I set it to disabled, I get something like :

<p style="margin-left:54.0pt;">Some text</p>
<p style="margin-left:54.0pt;">Some other text</p>
<p style="margin-left:54.0pt;">Another text</p>

If I set it to enabled, I get all the MS-Word clumsy code :

<p><!--[if !mso]>
<style>
v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
.shape {behavior:url(#default#VML);}
</style>
<![endif]--><!--[if gte mso 9]><xml>
  bla bla bla...
  bla bla bla...
  hundreds of lines...
  bla bla bla...
</xml><![endif]--><!--[if gte mso 10]>
<![endif]--></p>
<p class="Title4CxSpFirst" style="margin-left:54.0pt;mso-add-space:auto;
text-indent:0cm;tab-stops:35.4pt"><span style="font-size:11.0pt;mso-ascii-font-family:Calibri;
mso-hansi-font-family:Calibri;font-weight:normal;font-style:normal"><span style="mso-spacerun:yes">&nbsp;</span><span lang="EN-GB">Some text</span></span><span lang="EN-GB" style="font-size:11.0pt;mso-ascii-font-family:Calibri;mso-hansi-font-family:
Calibri;font-weight:normal"><span style="mso-spacerun:yes">&nbsp; </span></span></p>
<p class="Title4CxSpMiddle" style="margin-left:54.0pt;mso-add-space:auto;
text-indent:0cm;tab-stops:35.4pt"><span lang="EN-GB" style="font-size:11.0pt;
mso-ascii-font-family:Calibri;mso-hansi-font-family:Calibri;font-weight:normal;
font-style:normal">Some other text</span></p>
<p class="Title4CxSpLast" style="margin-left:54.0pt;mso-add-space:auto;
text-indent:0cm;tab-stops:35.4pt"><span lang="EN-GB" style="font-size:11.0pt;
mso-ascii-font-family:Calibri;mso-hansi-font-family:Calibri;font-weight:normal;
font-style:normal">Another text</span></p>
<p>&nbsp;</p>

The option is however set in Drupal.Settings :
"forcePasteAsPlainText":true
I don't get any javascript error.

Has anyone the same problem and/or solution?
I'm using the latest CKeditor (library) version : 3.6.3
And latest CKeditor module version : 7.x-1.9

Thanks!