This is not a bug. It is the polling timing which has been much discussed in the forums.
SmartThings polls the Hue Bridge approximately once every five minutes and gets the status of the bulbs at that time. This has been the known behavior for about a year.
If the bulbs are turned off by any means other then through the official smartthings connection, then it can take up to five minutes to see the updated status in smartthings. That’s all.
That includes turning them off via harmony, via echo, via a Phillips hue dimmer, via the official Hue app, via Beecon plus, via global cache, via a third-party app, etc.
It’s just how parallel means of control work with SmartThings and the Hue bridge.
Here is a link to one of the forum topics that discusses this.