My mistake. I know this doesn't matter since you found a better solution but this bugged me and I found my mistake.

I was thinking that the "=" in "<&=" was required when using a numeric file descriptor. But the "=" requests an fdopen() instead of a dup(), that is, the new file handle ends up sharing the same file descriptor with the old file handle. So when $fh is closed (triggered when it goes out of scope and gets destroyed), the file descriptor that DATA is using also gets closed out from under it.

So just drop the "=" and my code works.