You have some very good replies already. I would only add that perlcritic picks this up:

$ perlcritic 1178655.pl
Code before strictures are enabled at line 1, column 1.  See page 429 
+of PBP.  (Severity: 5)
Variable declared in conditional statement at line 5, column 3.  Decla
+re variables outside of the condition.  (Severity: 5)
[download]

If you have some odd-looking code like this which does not behave how you expect, perlcritic is a decent (but not infallible) tool to use in order to obtain some hints as to possible problems.