STM32U5 LTDC with 2 layers color keying seems to be ignored in final blending

[akj]

Seems like transparent background is ignored in final blending, any suggestions will be wellcome.
If key-coloring is changed on L2, background color will be shown, so I expect the key-coloring is actually working.
L1 has a background picture, and is not updated.
Changing L2 alpha from 0xFF to 0x80, normal blending showns both L1 and L2 in correct format, so data seems to be correct picked up.
L2 is updated pr. frame, double buffered, and is shown flawlessly but L1 is not visible, when L2-alpha is 255.

All Frame-buffers are in internal RAM and each in it's own RAM-bank alligned to 32 byte boundery.    

[akj]

Found that blending methode should be set for layer2 as:
    pLayerCfg.BlendingFactor2 = LTDC_BLENDING_FACTOR2_PAxCA;