What platform are you on?

On Windows when dealing with shared filesystems I have been burned enough that I routinely make sure that I have waited a substantial time (eg one second) between when I closed a file and when I do anything which depends on my write being visible to the world. Why this should be necessary I do not know, but then again I likewise don't bother to remember the exact combination of versions of Perl and Windows in which renaming a file from FOO to foo will delete the file because it does not realize that the target is the original file. (So delete the existing, then go to ren...oops.)

I merely know that I was burned and the absolutely safe fixes were to sleep in the one case or in the other to rename into another directory and then rename back. (Contrary to Microsoft's documentation on the bug, renaming through another name in the same directory was not safe.)

Anyways it is possible that you are hitting bugs...