Using RenderTexture Twice Clears the Previous Contents of the Texture (iOS only)

Unity Engine
,
1

I’m running into an issue with RenderTexture, on iOS-only builds.
I am doing a 2-pass render to the RenderTexture from 2 different cameras (code below).

The first pass looks like this:

384×512 168 KB

But on iOS, the second pass looks like this:

384×512 101 KB

The second pass completely obliterates the first pass.
I do not have this problem on Android/PC/Mac. Only iOS, newer hardware. It works fine on an old iPod Touch from 2012.

This is what it looks like on Android:

360×640 196 KB

And here is the code that does the two-pass render-to-texture:

    IEnumerator RenderScreenshot()
    {
        yield return new WaitForEndOfFrame();

        if (mInGameMenu == null)
            yield break;

        // The main camera is not showing a texture
        { // Render the main camera
            Camera mainCam = Camera.main;

            mainCam.targetTexture = Game.Instance.Script.ScreenshotTexture;

            if (mainCam.targetTexture != null)
                mainCam.Render();

            mainCam.targetTexture = null;
        }

        // The NGUI layer renders fine
        {   // Render the NGUI layer, with the screenshot elements

            GameObject nguiCam = GameObject.Find("UI Root/Camera");
            Camera uiCam = nguiCam.GetComponent<Camera>();
            uiCam.targetTexture = Game.Instance.Script.ScreenshotTexture;

            if (uiCam.targetTexture != null)
                uiCam.Render();

            uiCam.targetTexture = null;

            uiCam.depth = 0;    // Restore the camera depth
        }

        {   // Create the texture from the RenderTexture

            RenderTexture screenshot = Game.Instance.Script.ScreenshotTexture;
            RenderTexture.active = screenshot;

            int width = screenshot.width;
            int height = screenshot.height;

            Texture2D tex = new Texture2D(width, height);
            tex.ReadPixels(new Rect(0, 0, width, height), 0, 0);
            tex.Apply();
            Persistence.Instance.Mobile.Screenshot = tex;   // Save the screenshot
        }
    }

    // Screenshot logic is in UI, because we use the UI to render the watermark.
    private void TakeScreenshot()
    {
        // In case this is pertinent...
        GameObject nguiCam = GameObject.Find("UI Root/Camera");
        Camera cam = nguiCam.GetComponent<Camera>();
        cam.depth = -99;    // Hide the camera behind the other cameras

        ...

        // Use a coroutine to render a screenshot, because we have to wait
        // for the frame to finish rendering first.
        StartCoroutine("RenderScreenshot");
    }

Any ideas for fixes or workarounds? I’m almost convinced that this is a Unity bug…
Using Unity 5.3.1f1

EDIT:
And this is the related RenderTexture thread:
http://forum.unity3d.com/threads/rendertexture-not-working-on-ios-and-android-unity-4-2-0f4.192561/page-2#post-2498203

2

Bumping for more visibility on a Monday than on a Saturday.

I’m suspecting a bug in Unity, so if someone from UT can take a look, that’d be great.

3

Update: I couldn’t repro this with uGUI in a test project, so it’s probably not a Unity bug after all. I’m using NGUI, so I’ll approach it from that angle.