Bb3 Triangle Appears As A Square !

Hello-
I have been using BB2 for the past year and today is my first use of BB3, and I encountered a strange thing (hopefully it is not an issue in BB3 and I mis-configured something)

1. I created a new bbdoc using the 2D world
2. Inserted a triangle as an object (attached)
3. Pressed the play button
4. And now what is displayed in the preview window is a square

You can download the bbdoc file from here: https://drive.google.com/open?id=1JDl4RLbnp2mVB55f8fEo00o0K9vSNcx2
Any clues?

 

Update 1: The same issue is reproducible if I used a 3D world and switched to 2D from the top right 2D button, while testing the same image in BB2 it appears as a triangle normally

 

Update 2: On adding a 3D object to the same scene in the 3D world and run the preview again, now the 2D triangle appears as a triangle, now I am completely lost about this behavior, I was under the impression that it might have something to do with the camera position but now why adding a 3D object fixed the preview of the 2D object?

 

I see triangle in preview window in your bbdoc.

 

Hmmm, this is strange, I am using BB3 version 3.1.1 and the screen shot that I created is from my preview window, are you using the same version as mine?

 

Update 3: Just to add another point to the puzzle here, once I remove the 3D object the triangle stops being triangle and returns showing as a square in the preview window, so bottom line now if I have the 2D triangle on its own it appears as a square but if I insert a 3D object it appears as a triangle!

 

I captured this strange behavior in a video: https://drive.google.com/open?id=1j6MMDPVzgq3W59DdKyM3TU4BTjRMuR2x