This is behaving as expected: such CopyTexture calls are indeed unsupported and errors are printed to indicate this. As documented under Graphics.CopyTexture, "if you need to copy between textures with a different master texture limit, use the region-based overload".

However, the documentation around this is very obscure and we are looking into improving this; as the error messages don't seem to be particularly helpful in understanding why exactly things are going wrong. Especially the fact that 'setting Texture Quality' is the equivalent of setting a 'master texture limit' in scripts, is not at all made clear. Setting Texture Quality to half-res, quarter-res or eight-res is the equivalent of setting a master texture limit of 1, 2 or 3 for all Texture2D's that have a mip chain, meaning that 1, 2 or 3 highest-resolution mips are not uploaded to the GPU. Given that Texture2DArray does not currently support such master texture limits, CopyTexture cannot just work out of the box like this. Also, this support for master texture limit with Texture2DArrays is going to be investigated.