Chart Macro generates an incorrect URL instead of an image on sub-wikis

I tested the Chart Macro on a path-based farm using the following code:

(%id="table1"%)
|=|=X|=Y|=Z
|Q1|1.2|3.4|1.3
|Q2|4.5|3.4|2.3
|Q3|1.2|4.5|9.0
|Q4|3.4|1.2|1.2

{{chart type="bar" params="document:Sandbox.TestPage;table:table1;range:B2-D5;series:columns;" title="Chart Test" width="320" height="240"/}}

On the main wiki I got the correct image with the URL "http://localhost:8090/xwiki/bin/temp/space/page/chart/1949805868.png". On the FS the image is located in the folder "\Tomcat 6.0\work\Catalina\localhost\xwiki\xwiki-temp\temp\chart\xwiki\space\page" so no problem here.

On the "projects" sub-wiki I got an URL instead of the image pointing at "http://localhost:8090/xwiki/bin/temp/space/page/chart/2098136333.png". The image is not accessible because its location on the FS is not in "\Tomcat 6.0\work\Catalina\localhost\xwiki\xwiki-temp\temp\chart\xwiki\space\page" but in \Tomcat 6.0\work\Catalina\localhost\xwiki\xwiki-temp\temp\chart\projects\space\page".