I've never heard of Win32::AdvNotify, And at first glance i can't find any docs or it (since I can't find it on cpan) but based on this page i found on google it looks like you might want also want to print the event's "Action" ... i'm not sure what the actions will say, but it seems like it might be worth looking at.

I suspect that what is happening is that since you are monitoring an entire subtree, when you modify a file, you are getting an event for each of the directories above that as well (LAST_WRITE triggers an event for "Change in the modification date of a file or files")