use Switch;

Well, that's a likely problem right there. Source filters tend to introduce this sort of trouble. From the FAQ:

Starting from Perl 5.8, a source filter module, Switch, can also be used to get switch and case. Its use is now discouraged, because it's not fully compatible with the native switch of Perl 5.10, and because, as it's implemented as a source filter, it doesn't always work as intended when complex syntax is involved.