Coding for selective locking alters if only the driver door or all are opened with first unlock. So coding wouldn't explain the difference with both front doors opposed to rears. Front door locking is operated by individual door modules (P-bus message from body module) and rear doors by body module directly. So this sounds like a body module problem.

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E39 530dA -02 M-Sport Messing metallic
E53 X5 3.0dA -06 Sport Stratus grey
E70 X5 40d -12 M-Sport Space grey