Custom Expression Anomaly

[Tris]

Hi Guys,

I have a Custom Expression that is supposed to change the format of my
textbox to read only, but it is not. I copied the expression into a Rule, and
when it passed it displayed a text box saying Passed. This part worked as
correctly.

The purpose of the format is to make the price of Non machine items read
only if there is a Machine present. If the Machine quantity is set to 0, then
the non machine items should be modifable.

Can anyone explain why the Custom Expression would not work as a Conditional
Format, but works in a Rule?

XPath:
.../../myrder-line[my:is-machine = "1"]/my:item-qty = "1"

XML Schema:
<order-lines>
<order-line>
<is-machine>1</item-qty>
<is-machine>1</is-machine>
<is-machine>1000</item-price>
</order-line>
<order-line>
<is-machine>2</item-qty>
<is-machine>0</is-machine>
<is-machine>500</item-price>
</order-line>
<order-line>
<is-machine>1</item-qty>
<is-machine>0</is-machine>
<is-machine>500</item-price>
</order-line>
</order-lines>


* Both the conditional formatting and the rule are on the item-price node.
* The XPath Evaluates to True in the Rule Dialog, but does not make the node
read only.
* If i change the expression to 1=1 then the text box is read only.

Hope someone can shed some light on this.

Regards