Partly addressed, and I want to be straight about the rest. The panel really does draw two pendant slots and the second one is not wired — that part is real. But the second pendant slot is a LATER addition to MapleStory; v0.83, which this game is a 1:1 port of, has exactly one. So wiring it up would mean adding a mechanic the version we are porting does not have. I have fixed the slot map so the panel and the inventory agree, but I have deliberately not enabled a second equippable pendant. Your call: if you want the second slot as an intentional house rule I will build it and say so in the notes; if you want strict parity the right fix is to stop drawing the second slot at all. Tell me which and I will finish it.

Your v49 run said both slots accept a pendant and both count toward your totals, but that the Pendant of the Spirit gives no EXP buff in the second slot. That is fixed — the buff timer only ever looked at the first slot, so a pendant in the second box equipped, showed its stats, and silently granted nothing.

Wearing two does not stack, deliberately: the original bonus is a single per-character timer keyed to the item, not to the slot, so a second copy would be a mechanic that version does not have.

Your earlier question still stands unanswered though, and it is yours to decide: the second slot itself is a later addition. Keep it as a house rule, or stop drawing it for strict parity?