BUG with 4P ex-ram saving image

I use the OpenMV4P connet screen to display image.The screen pixel is not standard.So I use ‘sensor.alloc_extra_fb’ to creating a image,and zoom sensor.image to it for display.

Here is the BUG.In some complicated programs,the image screen display became strange.I tryed many ways,and found if I creating some empty image by 'sensor.alloc_extra_fb’before it,it fix.

Is the data in ex-ram conflict? Or my ex-ram has bad points?Or my program has BUG? I dont know.I get my temporary solution.But if it is your systems BUG,hope you can fix it.

Code? Please post the smallest snippet That causes the problem with code tags.