What interests me is how far the gust front appears to be ahead of the related clouds and moisture.
I noticed the gap behind the line first, before re-reading the earlier posts
I saw that as the interesting part.
My instinct is that the refractive effect due to air density changes would not be enough to cause phantom returns it -might- be sufficient to deflect weak returns.
Could it be that the clear area behind the line actually has precipitation that is hidden by the gust front?
Note: I am not at all a weather expert so don't know if this fits at all.