Here's the answer, and it's a bit confusing. A perl string has a magic bit attached to it, the UTF8 bit. If it is off, your string is assumed to be in latin1. That's fairly clear. What's not clear is that when the string is a bunch of utf8 chars, ö is considered a letter (for example), but when it's latin1 characters, ö is not a letter (unless using locale).

The solution is to make your strings utf8 strings, by using Encode.