Reproduction steps:
1. Open the attached project;
2. Build the scene "Test2";
3. Open built game and click Alt + Enter to switch fullscreen and windowed;
4. Observe the cube;

Actual result: when the window is switched from fullscreen and windowed view, the RenderTexture is destroyed and the cube becomes black.

Expected result: the RenderTexture should not be destroyed and the cube should have the texture.

Reproduced with: 5.3.7p4, 5.4.0f1, 5.4.4p3, 5.5.1p4, 5.6.0b6

Fixed from 5.6.0b7