I realise this is a very old thread, but I ended up here after google searching the same issue.
I too, had no key spawn in that location. However, thanks to someone's picture in this thread, I found the location and pressed the 'use' key there. I managed to pick up the invisible key!
Anyway, I registered an account just to let you know... if you even care anymore, or if others come to this thread with the same issue.
