Minecart causing observer pulsing

Description

When a minecart is placed on a diagonal rail facing into a fencegate or fence, if you place a piece of string on top of the fencegate or fence and attach an observer, it will cause the observer(s) to pulse continually.

 

How to Reproduce:

1. Place blocks like so:
2. Add a minecart onto the rail

 

Observed Results:

Observers continually pulse

 

Expected Result:

Observer pulses once when the minecart enters the string