Hello again,
I found the solution to the problem: all test cases I thought I had no output from had their project's resourceRoot property set to ${projectDir}. Obviously, this setting changes the base directory that is used when a path is constructed using maven-soapui-plugin's outputFolder setting. So the results for such projects were to be found inside the directory where the check out was made to and not the target folder.
Removing the resourceRoot property's value caused the correct relative path to be used and results were gathered as expected.
