Grimrock

Hello - I have one problem.

I clear up whole pyramid and get two keys. I used them on highest floor on lock - and teleporter appear in middle of room. When I kill few mobs and cleared room, I saved game and hope into teleporter... and I was killed very fast.
So I load game (teleporter was already opened, room cleared).
OK (I told myself) - it’s too early to get in that valley with hundreds of zombie and gigantic fire ogres.
So I leave temple and go to clear something else (more easy lands etc.).
BUT i have one problem now.
When I decided, there is good time to return back into pyramid (after many hours of playing elsewhere). I head back into pyramid (for entering opened teleporter on top floor and get into valley).
BUT !!! it is not possible anymore.
Understand me well – main entrance is still opened, but I can’t get through main doors on 2nd floor. Every door inside pyramid is locked and firmly attached now - so I can’t get back into valley of zombies (teleporter room is not accessible). I really want go back there - but I am unable to do it now.

Please can you give me some advice, what can I do now? Is it bug ?

if switch to this doors don't work so it must be bug

When I left the pyramid to level up before returning to Mummyland, the only doors closed were the ones leading to second floor, but since I left all the correct pressure plates pressed in the east and west rooms, all I had to do was push the four levers again to open the respective four grates and move on to the desert to fulfill my secret fantasy of killing a zillion mummies.

meteor storm makes short work of the mummies.