To reproduce:

1. Open the project, attached by user (RenderTexturesIssue.zip)
2. Open "Test" scene
3. Enter Play mode
4. Move Cube game object in the scene

Expected: no trail objects are rendered to the render texture when the texture uses the specific shader
Actual: copies of the object are renderer when the object is moved

Reproduced in 5.6.0a1, 5.6.1f1, 2017.1.0b6, 2017.1.0a1
Did not reproduce in 5.5.3p2
Regression introduced in 5.6.0a1

Won't fix: This was working before due to a side effect of how we passed the image effects texture into the OnRenderImage. This has changed now and the destination may not be implicity bound. You can fix this issue by binding the texture before doing the clear:

private void OnRenderImage(RenderTexture source, RenderTexture destination)
{
RenderTexture.active = destination;
GL.Clear(false, true, Color.black);
Graphics.Blit(rt, destination, postMat);
}