pwood999 said:

it's 1998. Not sure about EAS ECU revision though.

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On that year it should certainly remain in the locked position. Have you checked the white connectors in the passenger footwell at the bottom of the A post? The height selector wiring goes through there.
It is of course possible that the ECU has been changed at some time for an early one, even so I would have expected the inhibitor button to stop height changes.

My 97 works like Datatek`s, press button to lower to motorway then press inhibit and it stays there till you request a different height.

Connectors in left footwell have been removed & wires soldered years ago !! I'm not gonna worry about it as otherwise the system is working fine.