Losing properties from ant to webtest

Hi

We're using Webtest R_1812. We're losing properties from ant to webtest. 
After googling some time, I found that this issue might be related to the ant version. It should work with ant 1.71 but it does not. I tried also with 1.84

An example:

<project name="project name" basedir="." default="defaultTask">
...
    <target name="defaultTask">
        <echo message="property: ${invoke.url}" />
        <webtest name="Test something">

            <steps>
                <echo message="property 2: ${invoke.url}" />
 ...               
(some tests)
                ...
            </steps>    
        </webtest>
    </target>

...


The first echo will print the property content successfully.
The second echo prints the property name itself, which means, it's not set anymore.
So we're losing the property content from ant to webtest as it seems.

Thanks in advance for your help.