You're right. I bet perl is determining readability by calling access(2). From the man page: 
  access() may not work correctly on NFS file systems  with  UID  mapping
  enabled,  because UID mapping is done on the server and hidden from the
  client, which checks permissions.
and root_squash is a server option.

In reply to Re^3: -r broken on root_squash NFS? by pc88mxer
in thread -r broken on root_squash NFS? by zigdon

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