Can't mark certain posts as solutions

My bad, I do mean closing. The bug I’m reporting is this:

  • Make a thread that is capable of having a solution marked
  • Make a post in it
  • Close the thread
  • Make another post in it

The first post can be marked as a solution at any time. The second post can’t be marked. If you re-open and make another post that post can also be marked as a solution, but the post that was made while it was closed still can never be marked as a solution.