Phantom email notifications

I'm using Windows Live Mail (Version 2009) on my trusty old XP PC. When an email arrives I get an Incoming email ping, plus the email icon in the system tray turns to "You have new email", and when I go to the client I can see the incoming email. Just recently, on a couple of occasions (not every time) I get the incoming notifications but when I check the email client there's nothing there. I've checked through all my folders looking for something new, checked the Mail rules to ensure nothing's getting moved somewhere unexpectedly, logged onto my email accounts through webmail interfaces (both hotmail and other providers), but I cannot find any trace of any unread incoming email anywhere. So either WLM is generating phantom notifications, or it's cleverly deleting incoming emails from both my Inbox and Deleted Items box.

Any ideas what might be going on here - not least to reassure me that I'm not losing emails ? Any diagnostics I can try ?

Thanks in advance.