When my is encountered at run-time, a directive is placed on the stack to clear the variable. Since you're not executing my, the directive is not placed on the stack, so the variable doesn't get cleared.

The docs warn against using this side-effect of internal mechanics. (Emphasis in original.)

Note: The behaviour of a my statement modified with a statement modifier conditional or loop construct (e.g. my $x if ...) is undefined.

If you wish to have a static variable, use the following. (Surrounding curlies are optional.) 

{
   my $static;
   sub func {
      ...
   }
}

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See recent thread Lexical scope variable is not undef'ed.

In reply to Re: static variable hack by ikegami
in thread static variable hack by InfiniteLoop

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