If option -i is set to 1 (-i1) new png overwrite old though bigger size.
That is the intended behavior. I assume that users who specify -i1 expect the output image to be interlaced. OptiPNG obeys -i1 so that it always produces an interlaced image, even if compression gets worse.
It is unfortunate that interlacing almost always increases the file size. That is a shortcoming of PNG compression.
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