Its been noticed on several Direct access deployments that the Client IPHTTPS interface gets connected first over the Teredo interface although nothing is preventing the Teredo interface to get activated. Most of the clients won’t prefer the IPHTTPS because of its high overhead and low performance compared to Teredo or 6to4. After some investigation and consulting Microsoft esclation engineers it turned out that its a well known issue on several clients where the Teredo and IPHTTPS race together and IPHTTPS wins at the end due to timing issues. This is elaborated in details on the following Microsoft Technet article

As per that attached below image extracted from the above mentioned article that this issue can occur and IPHTTPS will win and get qualified first.

IPHTTPS qualify over Teredo due to timing issues

 To test whether my client is in this condition, i ran IPCONFIG /ALL on my client machine and i noticed that i have public addresses on both my Teredo and IPHTTPS interface as per attached.

Both IPHTTPS and Teredo interface have public IP address

To make sure you are using always Teredo you can implement one of the following workarounds:

  1. Disable IPHTTPSinterface from the Device Manager – View Hidden devices – Network adapters (unless you need IPHTTPS in locations where Teredo UDP port is blocked)
  2. After logging and connecting using the IPHTTPS, Restart the “IP Helper” Service.

For more information about this issue please check Tom Shinder article

Also its recommended to patch the UAG/Direct Access server with the latest fixes related to Direct Access, the most recent updates/fixes are as follows: