Orriginaly, I have specified the package gdm. But this package have been changed (by someone else) to xspash. Notes that this bug doesn't concern the first ubuntu boot step (only a ubuntu logo screened), but the second ubuntu step (ubuntu+logo+pseudo-progressbar). This second step appears when I restart gdm : that why I have specified the package gdm. The fist step of the ubuntu boot works well because the dual screen isn't already activated (X isn't started). I let this package to be xsplash because I am not a specialist...
Orriginaly, I have specified the package gdm. But this package have been changed (by someone else) to xspash. Notes that this bug doesn't concern the first ubuntu boot step (only a ubuntu logo screened), but the second ubuntu step (ubuntu+ logo+pseudo- progressbar) . This second step appears when I restart gdm : that why I have specified the package gdm. The fist step of the ubuntu boot works well because the dual screen isn't already activated (X isn't started). I let this package to be xsplash because I am not a specialist...