Twilight temple unable to re-open boss portal

As the topic suggests this is a problem related to the new unique map "The twilight temple".
The 3 sun plates and 3 moon plates were pressed, which unlocked the portal plates for the boss fights - here is where the problem appeared:

I accidentally ran over both plates, which caused the sun portal to appear and disappear, being replaced by the moon one. I entered and killed the moon boss without any problem, but upon returning to the plates I could not get the sun portal to open again - making me unable to complete the map.

Reference number: 717 178 750

Edit: Apparently you are only supposed to kill one of the bosses, after which the instance gets locked to that decision. This thread can be closed as it wasn't really a bug.