Event handler not found in when editing Dataset

-Guy-

I created a dataset with a beforeOpen event handler in Java, which is a request preprocessor. I put the corresponding jar in birt/scriptlib folder in org.eclipse.birt.report.viewer plugin.

This works fine when I run the report.

Now I want to edit my dataset. When I click on output columns tab or preview result tab, the request is executed, but the event handler class is not found.

I tried to put it in javascript using a script like this
importPackage(Packages.my.own.package);
process = new MyProcessClass();
process.execute(this);

Again, script works fine in preview, but when editing the dataset I get an error on the second line because MyProcessClass is not found.

Where do I have to put my jar so that it works when editing the dataset ?