I also noticed, after reading your post, this "bug".
Then I searched in the internet and found someone having the same issue: here
Open! Dammit, open up! I don't know why the gold door was so tetchy with me. Was I not standing in exactly the right place? Was the Enforcer on the other side stopping it from opening straight away? Was it a glitch that I unwittingly came across? Never mind, it's open now.
He posted a clip with a walktrough, showing all secrets.
Please watch this clip on position 6:40min.
This is the solution:
- Get the golden key
- Go to the golden door
- Walk right at the door, so that your nose touches it
- Now strafe left and right quickly.
Door will open short after.
It is really a bug. I dont know if its only in DP.
Hope I could help you.