First let us note that when the tax office is built, one gets the bonus to income whether or not the production que is empty. I recommend we do the following changes to the tax office (as it was probably intended)

The tax office is providing a wealth bonus when the production que is empty.. this should be changed to when the que is producing wealth.

The game modifier should be modified to something like this...

       <GameModifier>
            <ModType>ResourceMultiplier</ModType>
            <Attribute>Gold</Attribute>
            <Value>1</Value>
            <PerTurn>1</PerTurn>
            <IsProductionQueueEmpty>1</IsProductionQueueEmpty>
            <Provides>+25% Gildar when Producing Wealth</Provides>
            <Calculate InternalName="Calc" ValueOwner="OwnerCity">
                <Expression><![CDATA[[Constructing_ProduceWealth] * .25]]></Expression>
            </Calculate>
            <Calculate InternalName="Value" ValueOwner="OwnerCity">
                <Expression><![CDATA[[Calc] + 1]]></Expression>
            </Calculate>
        </GameModifier>