Problem was caused by different limits for "last" mipmap: it was 1x1 for mkaing mipmaps and 2x2 for re-making. 2x2 should be enough for mipmap.
Problem was caused by different limits for "last" mipmap: it was 1x1 for mkaing mipmaps and 2x2 for re-making. 2x2 should be enough for mipmap.