Prado - 4WD light staying on

I have noticed a small (hopefully) problem with my 97 Prado (auto). When I engage 4wd (via lever next to gearbox) it takes a while for the dashboard light to come on and confirm it is in 4wd. Also, when I disengage 4wd, it takes a while (approx 1 kms) for the light to turn off.

This happens when going from normal drive to 4wd H and back again. Yesterday, I had to stop, change thru to 4wd L, and back to normal before the light would go off. According to the Manual, I should be able to change on the move, without having to stop (although I usually stop).
Also, tried reversing a short way, but light would not go off. Eventually managed to get the light off by "jiggling" the 4wd lever whilst in Neutral (and chanting a few choice words at the lever).

Not a major problem last time as I was only in relatively firm sand, close to civilisation - hate for any problem to occur further a field!

Does the light mean I am in / out of 4wd? or does the lever mean i am in / out 4wd??
Do a have a major (read expensive) problem, or could it be a simple (known) fault?

Any help would be appreciated as I am soon to have 2 weeks off and would rather spend them exploring a few local tracks, rather than sitting in a mechanics waiting room.

Thanks in advance

RD