From what I can see that's a bug in the perl interpreter. It gives incorrect output for at least 5.8.6 (threaded), 5.8.7 (debug, nonthreaded) & 5.8.8 (threaded)

update: it gives

Checking for pause...
Can't use an undefined value as a subroutine reference at test.pl line
+ 8.
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For perl 5.00504