weird delay thuderbird and samba

[Linda]

I have a small network includes mostly ubuntu/lubuntu boxes and 2 windows 7 machines. I am having a strange issue thought someone might have a suggestion on to trouble shoot it.
We have a directory that is shared to the linux computers with nfs and the windows computers with samba. When the user wants a pdf for output it puts it in that directory. When the user creates  the pdf and thunderbird is not open the file immediately appears in the directory just like it does on the linux boxes, but if thunderbird is open the file does not appear in the direcotry for the windows user. If they close thunderbird and reopen the directory it is there. Any idea what might cause the delay and how to fix it?
                      Thanks
                     Linda