I just recently did something like this, and it writes it properly, I am still having issues with the loading of weapons though, but I use this code everywhere I want to save... may be a little clunky, but I like seeing what the code is :P
pawn Code:
//Save Weapons and Ammo
GetPlayerWeaponData(playerid, 0, PlayerInfo[playerid][pWeapon0], PlayerInfo[playerid][pAmmo0]);
GetPlayerWeaponData(playerid, 1, PlayerInfo[playerid][pWeapon1], PlayerInfo[playerid][pAmmo1]);
GetPlayerWeaponData(playerid, 2, PlayerInfo[playerid][pWeapon2], PlayerInfo[playerid][pAmmo2]);
GetPlayerWeaponData(playerid, 3, PlayerInfo[playerid][pWeapon3], PlayerInfo[playerid][pAmmo3]);
GetPlayerWeaponData(playerid, 4, PlayerInfo[playerid][pWeapon4], PlayerInfo[playerid][pAmmo4]);
GetPlayerWeaponData(playerid, 5, PlayerInfo[playerid][pWeapon5], PlayerInfo[playerid][pAmmo5]);
GetPlayerWeaponData(playerid, 6, PlayerInfo[playerid][pWeapon6], PlayerInfo[playerid][pAmmo6]);
GetPlayerWeaponData(playerid, 7, PlayerInfo[playerid][pWeapon7], PlayerInfo[playerid][pAmmo7]);
GetPlayerWeaponData(playerid, 8, PlayerInfo[playerid][pWeapon8], PlayerInfo[playerid][pAmmo8]);
GetPlayerWeaponData(playerid, 9, PlayerInfo[playerid][pWeapon9], PlayerInfo[playerid][pAmmo9]);
GetPlayerWeaponData(playerid, 10, PlayerInfo[playerid][pWeapon10], PlayerInfo[playerid][pAmmo10]);
GetPlayerWeaponData(playerid, 11, PlayerInfo[playerid][pWeapon11], PlayerInfo[playerid][pAmmo11]);
GetPlayerWeaponData(playerid, 12, PlayerInfo[playerid][pWeapon12], PlayerInfo[playerid][pAmmo12]);
INI_WriteInt(File,"Weapon0",PlayerInfo[playerid][pWeapon0]);
INI_WriteInt(File,"Ammo0",PlayerInfo[playerid][pAmmo0]);
INI_WriteInt(File,"Weapon1",PlayerInfo[playerid][pWeapon1]);
INI_WriteInt(File,"Ammo1",PlayerInfo[playerid][pAmmo1]);
INI_WriteInt(File,"Weapon2",PlayerInfo[playerid][pWeapon2]);
INI_WriteInt(File,"Ammo2",PlayerInfo[playerid][pAmmo2]);
INI_WriteInt(File,"Weapon3",PlayerInfo[playerid][pWeapon3]);
INI_WriteInt(File,"Ammo3",PlayerInfo[playerid][pAmmo3]);
INI_WriteInt(File,"Weapon4",PlayerInfo[playerid][pWeapon4]);
INI_WriteInt(File,"Ammo4",PlayerInfo[playerid][pAmmo4]);
INI_WriteInt(File,"Weapon5",PlayerInfo[playerid][pWeapon5]);
INI_WriteInt(File,"Ammo5",PlayerInfo[playerid][pAmmo5]);
INI_WriteInt(File,"Weapon6",PlayerInfo[playerid][pWeapon6]);
INI_WriteInt(File,"Ammo6",PlayerInfo[playerid][pAmmo6]);
INI_WriteInt(File,"Weapon7",PlayerInfo[playerid][pWeapon7]);
INI_WriteInt(File,"Ammo7",PlayerInfo[playerid][pAmmo7]);
INI_WriteInt(File,"Weapon8",PlayerInfo[playerid][pWeapon8]);
INI_WriteInt(File,"Ammo8",PlayerInfo[playerid][pAmmo8]);
INI_WriteInt(File,"Weapon9",PlayerInfo[playerid][pWeapon9]);
INI_WriteInt(File,"Ammo9",PlayerInfo[playerid][pAmmo9]);
INI_WriteInt(File,"Weapon10",PlayerInfo[playerid][pWeapon10]);
INI_WriteInt(File,"Ammo10",PlayerInfo[playerid][pAmmo10]);
INI_WriteInt(File,"Weapon11",PlayerInfo[playerid][pWeapon11]);
INI_WriteInt(File,"Ammo11",PlayerInfo[playerid][pAmmo11]);
INI_WriteInt(File,"Weapon12",PlayerInfo[playerid][pWeapon12]);
INI_WriteInt(File,"Ammo12",PlayerInfo[playerid][pAmmo12]);