[Zope] Acquisition bug ?

Hi, I got a MailHost object at /site/MailHost that's used successfully from objects in /site subfolders. There's a particular folder /site/subscribe from which there's no way to use this MailHost (object not found). I can't understand cause there are no special security features in that MailHost or in that particular folder! In addition, DTML documents from that folder, including the one that has the <dtml-sendmail mailhost="MailHost"> can acquire other objects from /site like the standard_html_header. The only workaround I found is to make a copy of this MailHost in /site/subscribe. Any hint ? Regards --Gilles