wowapi GCD deviation

[Immortalhz]

Havent noticed this behaviour before, but it is what i get today
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code is

Start, CD, enabled, modRate = GetSpellCooldown(61304)
print("Left = "..getSpellCD(61304)..". Start = "..Start..". CD = "..CD..". GetTime = "..GetTime())

function getSpellCD(SpellID)
    local Start, CD = GetSpellCooldown(SpellID)
    if CD == 0 then
        return 0
    end
    local MYCD = Start + CD - GetTime()
    if MYCD >= 0 then
        return MYCD
    elseif MYCD < -1111 then
        return 111
    end
end

when i just spam any gcd skills, sometimes it just gives me wrong info, gcd is 0.9+ and next frame we dont have gcd, its minor issue, but still interesting if anyone expiriences this and how to make workaround, i ran out of ideas