Hi Bruno,
I wasn't able to reproduce this. I set up the following 3 properties with a vanilla Orbeon Forms 4.1, and when I hit the "submit" button, the dialog shows up with just one button. So I am not sure what the difference is in your case, maybe you could try using a clean build and see if you can reproduce this there?
<property as="xs:string" name="oxf.fr.detail.buttons.orbeon.controls" value="submit"/>
<property as="xs:string" name="oxf.fr.detail.submit.buttons.*.*" value="go"/>
<property as="xs:string" name="oxf.fr.detail.submit.go.uri-xpath.*.*" value="'
http://www.orbeon.com/'"/>Alex
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