Break lines with <br>

In the editor, when I do a "enter" I have a single line return.
If I look at the code, it is <br />

When I display that text in a page , the code is :
<br><br>

twice <br>

And I found no way to have a simple return (a single line)

In the JS config, I put :
FCKConfig.EnterMode = 'br' ; // p | div | br
FCKConfig.ShiftEnterMode = 'br' ; // p | div | br

Any help, thanks you.
Pierre.