Set TC Parameter with Service Message from within a Meta-Runner, TC 2020.1

See subject - this just doesn't seem to work and I haven't been able to find any information.

I've created a minimal test build where I set a teamcity parameter from a runner (tested command line on linux and powershell on windows) doing something like (service message functionality):

echo "##teamcity[setParameter name='testparam1' value='value_from_service_message_main_build_config']"

and then in the next build step:

echo "testparam1=%testparam1%"

works fine in every combination/version in the main build, but if I do exactly the same in my meta-runner the parameter is simply not set (retains default value).

Any ideas?! Many thanks!