disappearing upload button with IE

i have a strange behaviour... if i load a form for a cck content, with multiple file uploads allowed, thanks to filefield, the upload button (CARICA in the attached screenshot) is not visible at first... i need to go with mouse cursor on the cross on the left, and THEN the button appears... but if i go on the "add an other item" (AGGIUNGI UN ALTRO ALLEGATO in the attachment to this issue), they disappear again... latest firefox and chrome do not have this problem, but internet explorer yes, at least version 8...