The reason why you see the erasures prior to an image being drawn is due to the smart erase feature. This automatically adds an erase animation when an image is on top of another. To turn it off, simply click Settings, above the timeline. Then, within the Video settings set erase mode to off.
You can also change the scene transition to not have an erase animation.
Alternatively, if you wish to turn the erase function off for specific assets, you may do so through the image settings.
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