joodb creates 2 records on submit

i build first in xammp localhost a database and all the records were added twice. So i build it into my live surrounding ( joomla 1.5.22 stable) but again every record is added twice into the database.
Anyone a suggestion?

in firefox 3.6 the submit button delivers one new entry. In Internet explorer 8.0.6001 (no compatibilitymode) it creates 2 new records after submitting a form.

Found this on the internet, does it ring a bell?
Recently I faces a problem in admin module, developed by some programmer that when I submit add entry button it adds two records but when I submit for Firefox, I was working fine.
After 3 hour of mess I found error, In IE8 you have to return false, if you are submitting form through javascript. Here is example
<form name=”frm” onsubmit=”return chkForm();”>
function chkForm()
{
//Variuos checks
document.frm1.submit();
return false;
}