Is that limitation documented somewhere? The perlfork docs seems to imply that they do can be separate.

   Open handles to files, directories and network sockets
           All open handles are dup()-ed in pseudo-processes, so that
           closing any handles in one process does not affect the othe
+rs.
           See below for some limitations.
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Here's the caveat that follows.

   Open filehandles
           Any filehandles open at the time of the fork() will be dup(
+)-ed.
           Thus, the files can be closed independently in the parent a
+nd
           child, but beware that the dup()-ed handles will still shar
+e the
           same seek pointer. Changing the seek position in the parent
+ will
           change it in the child and vice-versa. One can avoid this b
+y
           opening files that need distinct seek pointers separately i
+n the
           child.
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