A locked door in Labyrinth and no other way to get there

My first trial of Labyrinth and I got stuck at one map which branches into two rooms.

Situation :

- Let's say the map I am stuck as A, and the next two rooms as B and C
- I proceeded to B
- It was a silver door room and used one silver key
- Came back to A
- I found another way which is assumed to be the way to C
- I found a igniting floor trap with three levers and activated all three levers
- And then I am stuck at this locked door + there seems no other way to get there + not able to get back to the former room of A



Did I missed something or is this an intended feature?


bug report reference number : 4169057042

Nvm. I found a stair to get through at right side.