Minecart with furnace turns diagonal on straight rail

Minecart with furnace turns diagonal on a straight rail

 

What I expected to happen:

It would continue to face 'forward'

 

What actually happened:

It turned diagonal spontaneously as shown in pictures 2 & 3

 

Steps to reproduce:

1) Build the 10*3 track shown in picture 1

2) Place a minecart with furnace

3) Fuel the furnace