Detector rails don't auto-rotate when placed under a minecart

Looks like they activate first and then forget they were supposed to connect.

How to reproduce:

1. create a line of at least two rails (probably of any type, haven't tested with others than normal) going east to west (this is important)
2. drive a minecart off one end, make it sit right next to it.
3. place a detector rail under the minecart.
4. observe