Hi Narval,
When you loose the AP, the plane has a natural desire to climb...
The only aircraft I know which did that was the L1011 during an Auto Land Approach. (AL selected)
Every other aircraft I've flown, when the AP drops out, remains in trim and continues along the same trajectory. I can confidently report that's true for the A320 series in Normal Law. (If it does what it says on the tin - then it should be the same in ALT LAW also)