Thermaltake Armor+MX: Stand-off Hole Too Small

When screwing in the standoffs for the motherboard in this case, the last hole needed would not accept a standoff. It would only screw in one turn, leaving the majority of the thread still exposed.

According to the manual this hole should take a stand-off. Also, there is a hole on my motherboard correlating to the hole site in the case. The only thing I can visibly separate between the holes that accept standoffs and the one that doesn't is labeling beside them. Acceptor sites have AFM while the one that won't screw has only AF.

Is there something I'm missing here or could this be a factory defect? Also, is one missing standoff even an issue, especially when ist in the lower corner of the motherboard?