I have seen these symptoms on some of my ILS approaches but it's been more a problem with the pilot than the autopilot.

A couple of times I've disengaged the AP and, then to slow down even more, I hit the spoiler.  The result is that the nose pitches up because the spoiler extends up out of the wing and acts like the elevators.

The other way I have managed to do it is on the AirBus.  It acts as though it reverts to the joystick throttle setting instead of staying where the ias hold was set.  This makes sense because the joystick throttle was set above the ias hold.  However, I haven't seen it to the same degree on the default planes.

gw

   I have never had a problem where the plane pitches up or down a whole lot it might move plus or minus 50 or so feet, but that is no big deal. I always disengage the autopilot while I am in straight and level flight and not desending. If you disengage autopilot while desending I could see where you might have a problem. All aircraft use a different default rate of climb or descent, which can be any where from 750 to 18oo feet per min. If you are desending at 1800 feet per min and dis engage the autopilot it could very well go back to the last trim you had set while not in autopilot resulting in a drastic pitch up or down of the aircraft. Also do not forget to check your autothrottle setting and joystick throttle setting if you have one or do not use the keypad for throttle control. If you use a joystick to control throttle you more or likely left in at or close to max power from takeoff.  Then when you lower your airspeed to at or below 25o below 10,000 feet then swithch off autopilot the engines will go back to full throttle which will cause the aircraft to climb. The main reason I stopped using my joystick for throttle control and I found reverse was not working right with joystick control.

Try fooling the autopilot.
When you are about to disengage the AP, gently pull up on the stick, enough to simulate the degree of lurch you usually get; the autopilot should retrim elevators to maintain proper attitude (that is, it should set them downwards because you are pulling up). Press Z and release the stick at the same time. If the autopilot sets the trim relative to descent rate instead of some arbitrary degree, you should still be descending, or at least minimize the lurch.

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Thank you!
How people can compare spoiler to elevators, flaps, old grandmas etc is beyond me  ???  

Flaps are not spoilers. True that flaps disturbs the airflow and spoilers do the same. but flaps creates more LIFT, spoilers do NOT...in fact they do the opposite