glCopyImageSubData issue

[mode89]

Hello, everyone!

I've experienced a problem with glCopyImageSubData. I try to copy a compressed DXT1 2D texture array to another compressed DXT1 2D texture array with the same dimensionality. All mip levels copied except the two smallest (1x1 and 2x2) - they stay unchanged (in the destination texture) after copying.
Why does it happen?

for (int level = 0; level < levelCount; ++ level)
{
    int mipWidth  = GetTextureMipWidth(srcTex, level);
    int mipHeight = GetTextureMipHeight(srcTex, level);
 
    glCopyImageSubData(srcTex, GL_TEXTURE_2D_ARRAY, level, 0, 0, 0, dstTex, GL_TEXTURE_2D_ARRAY, level, 0, 0, 0, mipWidth, mipHeight, arraySize);
 
    glBindTexture(GL_TEXTURE_2D_ARRAY, dstTex);
    glGetCompressedTexImage(GL_TEXTURE_2D_ARRAY, level, dstData);
    glBindTexture(GL_TEXTURE_2D_ARRAY, 0);
}

Thanks