I am guessing they have a customized (or out of date) PlayerCorpse.cpp.
With the latest version of source, I was able to get loot window to appear by adding one line to Corpse::MakeLootRequestPackets()
Code:
else if(GetPKItem() == -1 && CanMobLoot(client->CharacterID())) { tCanLoot = 3; } //pvp loot all items, variable cash
else if(GetPKItem() == 1 && CanMobLoot(client->CharacterID())) { tCanLoot = 4; } //pvp loot 1 item, variable cash
else if(GetPKItem() > 1 && CanMobLoot(client->CharacterID())) { tCanLoot = 5; } //pvp loot 1 set item, variable cash
else if (lootcoin) { tCanLoot = 6; } // Added by Alecta, just cash, no items.
Adding that bottom line will let the code fall through the checks to generate the ItemPacketLoot but since GetPKItem()==0 you can't actually loot anything in Corpse::LootItem().
If a developer wouldnt mind providing me with the P1999 PlayerCorpse.cpp, I could diff it up and see what's going on.