Are Assembly.Load and Assembly.LoadFrom differences?

Question

My application loads the assemblies it needs through an event AppDomain.CurrentDomain.AssemblyResolve. Assemblies are the resources of the executing assembly.

private static Assembly OnResolveAssembly(object sender, ResolveEventArgs args)
{
    var executingAssembly = Assembly.GetExecutingAssembly();
    var assemblyName = new AssemblyName(args.Name);
    var resPath = assemblyName.Name + ".dll";

    using (var stream = executingAssembly.GetManifestResourceStream(resPath))
    {
        if (stream != null)
        {
            byte[] buffer = new byte[stream.Length];
            stream.Read(buffer, 0, buffer.Length);

            return Assembly.Load(buffer);
        }
    }

    return null;
}

This works fine overall, but the downloadable assembly contains default styles for certain controls that will not apply. BUT, if I do not load the assembly through Assembly.Load, but save it to a file and load through Assembly.LoadFrom, everything works fine.

What is the difference between the two? Why doesn't it work when loading an assembly directly from memory - or why does it work when it first saves it to disk and then loads it with Assembly.LoadFrom?

I am very confused and I want to load assemblies directly from memory without saving them in the first place.