That is because your aftermarket deck is piggy backing off the stock harness. With the stock radio still in the loop, everything functions properly.
If you cannot locate the code in your service manual, you can contact the dealership. You will need the ID numbers off the factory radio. With these codes, the dealer can give you the code to unlock the radio.
Wrong. Don't share incorrect information.
Chances are you had this professionally installed and the installer jumped the two correct pins in the security harness to complete the circuit and allow the dome light to function or you have the scosche wire harness that also includes the jumper plug.
Correct. Factory keyless entry is also tied into the factory radio. In order to keep this function, you will need to relocate your factory radio, either with a T harness that will allow the aftermarket radio to operate while also keeping the factory radio connected, or with the scosche radio relocation harness.
It does not mean your deck was necessarily installed wrong, it just means your installer is either uninformed of the issue, or neglected to read the notes on the dash kit's installation tips. Probably both. Regardless, you can easily remedy this issue. Either, order the scosche wire harness which includes the security harness cap which jumps the correct wires, or jump the wires yourself. I believe the link above contains the picture or link to the correct wires in the security harness.