All hidden mechanisms in certain places (sewers, for instance) do not disappear from sight again after a while, upon being found.
This has either not been fixed for a long while, or it is reoccuring.
ALL hidden mechanisms?
I can well imagine if a new one has been added by certain newbie DMs it might not properly reset, but if you mean to say that all secret doors are not disappearing that is another matter.
Can someone confirm?
The one in the Sewers indeed doesn't disappear after being found, and it lingers visible until there's a reset.
But I do know of at least two hidden doors in other areas that work just fine, and disappear after a short while like they should
It is the situation for all hidden mechanisms in the Sewers. That's all I can confirm.