You didn't specify the model year of your car (yes, this can make a difference). One would assume that this feature would be universally standard. Did the hazard indicator flash twice when you attempted this?
According to these instructions, if you disable the autolock feature and manually lock your doors, the locks will not automatically unlock when the ignition switch is placed in the OFF position.
Section 3-5
All doors lock automatically when the vehicle speed reaches 15 MPH (24 km/h).
All doors unlock automatically when the ignition switch is placed in the OFF position.
The automatic unlock function can be deactivated or activated. To deactivate or activate the automatic door unlock system, perform the following procedure:
- Close all doors.
- Place the ignition switch in the ON position.
- Within 20 seconds of performing Step 2, push and hold the power door lock switch to the position (UNLOCK) for more than 5 seconds.
- When activated, the hazard indicator will flash twice. When deactivated, the hazard indicator will flash once.
- The ignition switch must be placed in the OFF and ON position again between each setting change.
When the automatic door unlock system is deactivated, the doors do not unlock when the ignition switch is placed in the OFF position. To unlock the door manually, use the inside lock knob or the power door lock switch (driver’s or front passenger’s side).
The automatic door unlock function can be changed on the lower display. (See the Infiniti InTouch Owner’s Manual.)
Also in section 8-22 of the In-Touch manual.