It is difficult to guess what is causing this. Maybe you post here the full information about your Office - version number (the long one), 32 or 64 bit, are you using it in domain, are you creating a workbook on network resource or in your hard disk, etc. Then maybe there will be someone with build like yours, who can write how it works for him/her. When it is same, then it is Office problem, otherwise the cause is local.