jQuery 1.10.1 setting non existing value on select

Answer 1

Using the jQuery 1.10.1 the value of the select is null, but using jQuery 1.9.1 the value is the first option.

It's the fix to bug #13514, fixed in v1.10. Setting an invalid value should clear the select (which it does in v1.10+), not leave it at the default (first) option (v1.9).