The issue:
Same rail design doesn't works the same depending on it's orientation - only works as intended on north-south orientation (see attached video where the first run is done on the design orientated north-south and works as expected).

On east-west orientation, the Activator Rail after the curve is apparently activated sooner than it's north-south counterpart, making it go straight instead of going to the other direction. The same doesn't happens on north-south orientation as the cart makes the turn as expected.

The design:

They're the same design, just rotated 90 degrees. The one to the right is the north-south orientation.

Angle 1/2:

Angle 2/2:

Thoughts:
I have no idea what's causing the difference in behavior due to orientation changes. Maybe a redstone peculiarity, if so, I apologize for the mistake.

It seems to me that the issue is that the hitbox for the Minecart is nudged when there's a curve, which activates the Activator Rail on the next block - although the reason why the design works on one specific orientation is beyond me. 

Minecart's hitbox right after it's placed:

Minecart's hitbox adjusted for the curve:

 
EDIT: Fix below seems to not be working, actually.

Temporary design fix (maybe this helps):
To temporarily fix the design I added this turn:

Any smaller turns don't work and make the cart ignore the entrance, so for the cart to not take the track where the redstone block is there should be at least 2 straight blocks perpendicularly.