IsSpellUsable buggy ?

I'va add the following sequennce to my Combat Rogue Profile. Without "IsSpellUsable" it works fine, but spams Stealth, if it is not ready. With "IsSpellUsable" it do nothing ?!?

(the buildin CheckIfKnowUsableDistance I couldnt use, because stealth doessn't need a target)

    <FightClassSpell>
      <SpellName>Stealth</SpellName>
      <FightClassConditions>
        <FightClassCondition>
          <ContionType>Buff</ContionType>
          <Param xsi:type="FightClassConditionStringBool">
            <Name>Stealth</Name>
          </Param>
        </FightClassCondition>
        <FightClassCondition>
          <ContionType>HostileUnitNear</ContionType>
          <Param xsi:type="FightClassConditionUnitNear">
            <Type>Bigger</Type>
            <Radius>30</Radius>
          </Param>
        </FightClassCondition>
        <FightClassCondition>
          <ContionType>LuaScript</ContionType>
          <Param xsi:type="FightClassConditionLua">
            <LuaScript>if UnitIsPVP("player") or (UnitInParty("player")==nil) then retV=1; end</LuaScript>
            <VarRet>retV</VarRet>
            <ValueRet>1</ValueRet>
          </Param>
        </FightClassCondition>
        <FightClassCondition>
          <ContionType>IsSpellUsable</ContionType>
          <Param xsi:type="FightClassConditionStringBool">
            <Name>Stealth</Name>
            <Need>true</Need>
          </Param>
        </FightClassCondition>
      </FightClassConditions>
      <Priority>6</Priority>
      <CombatOnly>false</CombatOnly>
      <CheckIfKnowUsableDistance>false</CheckIfKnowUsableDistance>
      <CheckIfView>false</CheckIfView>
      <DescriptionSpell>Stealth if hostile 30 Yards away. only pvp or solo</DescriptionSpell>
    </FightClassSpell>