Help with a Secret Stair glitch?

[noname]

I've finished the story mode and now I'm freeplaying to get the rest of the achievements.

I just finished the Secret Stairs, and for some reason, when I picked up the third treasure (the spider's fang), It showed in my pause menu as 4/3 treasures found. When I exited the level, it counted like there were four treasures, and ticked back over to 1/3 treasures, so I didn't get the mithril brick. I've tried replaying it again, but since I already have the treasures in my inventory, I just get a stud instead of the actual item.

Is there any fix, or does anyone have any advice? I really don't want to start a new game now that I'm about 70% done.

[MrsKryten]

Check out the discussion at http://steamcommunity.com/app/214510/discussions/0/828925849519294103/ as I've posted a link to a forum that may be helpful. It talks about the same 4/3 glitch but in a different level.