It's also only woks with ">" and ">=" comparators
"<" and "<=" not working

Which class and spec? Can you provide a sample script?

any class or spec
last tested on elemental shaman
script below is working when GCD triggered by instant cast spell, but not working when GCD triggered by casting spell

AddIcon
{
if GCDRemaining() > 0.5 Texture(spell_chargenegative)
}

script below not working with all type of spells

AddIcon
{
if GCDRemaining() < 1 Texture(spell_chargenegative)
}

I don't understand the bug. There shouldn't be any global cooldown after a spell has been cast if it isn't an instant cast

Here is example script for any pally.
so basically i want to cast avenging wrath on last 0.5 second of gcd since it off gcd
but it will be be shown for the next action even when gcd remaining is more then 0.5

may be i misusing this function?

Define(avenging_wrath 31884)
SpellInfo(avenging_wrath cd=120 offgcd=1)
Define(flash_of_light 19750)

AddIcon
{
if GCDRemaining() < 0.5 spell(avenging_wrath)
spell(flash_of_light)
}

The functions are always computed at the end of the current cast. It means that if there isn't any global cooldown after the current cast (which is always the case for spells with a cast time), GCDRemaining will be always 0.

but example script does not work even when i use instant cast spell to trigger GCD . avenging wrath seen as next action full GCD duration

Ok, I'll check into this

RemainingCastTime also buged.
RemainingCastTime()<1 works sometime and then never return true.
RemainingCastTime(less 1) - same result.
not RemainingCastTime()>1 will work (idk correct or not)

checked again, bug is still there