What? It seems to me that Z* does stop at the zero byte, it's only Z with a finite number that does not stop. Look.

$ perl -we '($a,$b)= unpack "Z*a*", "nine\0eight"; warn ">>$a<< >>$b<<
+";'
>>nine<< >>eight<< at -e line 1.
$ perl -we '($a,$b)= unpack "Z8a*", "nine\0eight"; warn ">>$a<< >>$b<<
+";'
>>nine<< >>ht<< at -e line 1.
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This was with perl, v5.8.1 built for i686-linux.

Update: just checked, with perl 5.6.1, I get the wrong behaviour, that is, Z* consumes all the string.