Yup, I get a similar effect in Perl v5.6.0 built for darwin -- it leaks unless there's an explicit close().

In fact, if you let the test script run long enough, it eventually runs into some other kind of problem on repetition number 252; perhaps it's running out of file handles? perl -w -l -e 'BEGIN {print "$$\n"} while ( 1 ) { do "file_with_DATA.pl"; print( ( ++ $i ) . ": " . `date`, ` ps -o rssize $$` ) }'