Script problem/creation bookmark

Hi,
 
I'm having strange problem when creating a bookmark within js code of a stamp.
(Idea is to create a bookmark to the page where stamp is posted)
 
Stamp has two user-entry fields, but that part working well..
 
but bookmark creation - doesn't do anything (no errors as well).
 
if(event.source.forReal && (event.source.stampName == "#bf"))
{
if ("ok" == app.execDialog(dialog))
{
var cMsg = dialog.LValue.substr(0,5);
event.value = cMsg;
cMsg = dialog.UValue;
this.getField("U").value = cMsg.substr(0,5);
console.println(event.target.doc.pageNum); //debug
event.target.doc.bookmarkRoot.createChild("qwerty", "this.pageNum=0", 0);
}
}
 
Any suggestions?