GetCompanionInfo("MOUNT") broken for WotLK Classic 3.4.3?

[fullmoon_sulfuras]

GetCompanionInfo seems broken when getting mount information on WotLK 3.4.3. The following snippet works:

for i=1,GetNumCompanions("CRITTER") do
    local creatureID, creatureName, creatureSpellID, icon, issummoned = GetCompanionInfo("CRITTER", i);
    print(creatureID, creatureSpellID, creatureName, icon, issummoned)
end

However, this returns all nil values:

for i=1,GetNumCompanions("MOUNT") do
    local creatureID, creatureName, creatureSpellID, icon, issummoned = GetCompanionInfo("MOUNT", i);
    print(creatureID, creatureSpellID, creatureName, icon, issummoned)
end

My addon's code is very similar to the snippet above and used to work fine until 3.4.3.

The odd thing is that in Interface_Wrath/FrameXML/PetPaperDollFrame.lua there's:

function PetPaperDollFrame_OnLoad (self)
    self:RegisterEvent("PET_UI_UPDATE");
    self:RegisterEvent("PET_BAR_UPDATE");
 
    ...
 
    PetPaperDollFrameCompanionFrame.mode = "CRITTER";
    PetPaperDollFrameCompanionFrame.idMount = GetCompanionInfo("MOUNT", 1);

Any ideas are more than welcome! Thanks!!