Can not Interact with a Draiocht Hengestone

Just killed the map boss in the Molten Vault. There is a Draiocht Hengestone next to me but I am unable to interact with it in any way. Buggged!

[Edit update] After posting this original bug report, I logged off for a bit, then came back and ran the same map again (the game let me). This time, after killing the map boss, the game allowed me to interact with the Draiocht Hengestone. This suggests that the bug is an intermittent phenomenon.

Please fix. Thanks.