Monogame Rendertarget switching error.

Hi, i use monogame hosting on WPF , that render direct3D on a image.
I use only 2D graphics.
This library use 2 files “sharpdx.Direct3d9.dll” and “SharpDx.dll” both are versions and MonoGame last version libraries.
I’ll making render to texture, using RenderTarget2D, so i need switch the RenderTarget on a GraphicsDevice.
When i’m trying to switch RenderTarget in code,
GraphicsDevice.SetRenderTarget = null; // render direct on a framebuffer
i got nothing rendered on a screen in next spritebatch.draw()
When i make just code like that:
I got the proper RenderTarget switching.
But in a MonoGame standalone app RenderTarget switch immidiately and fine, as will be.

Ohh, too long explanation.
I know, that the host of monogame isn’t part of monogame and was created non-party peoles, but, guys, if you know that peoples, maybe you can give me contacts of authors of that WPF-hosting, or advice maybe another one hosting 9i didn’t find in internet another solution). Please, advice me how i can get proper RenderTarget changing without delays. Ty for participation.

Solved. Very strange bug, but all works propertly where i create images on a rendertargets2d in methid “Update()” and in method “Draw()” i do only “Gluing layers” of my scene on one surface (i mean backbuffer). In this ыуйгутсу фдд цщклы ашту фы ш цфтею