JavaSampler doesn't set a sampler label as most other sampler implementations do. This causes Aggregate Report results from types that implement JavaSamplerClient to be grouped together.
Created attachment 18845 [details] JavaSampler.sample now sets the sampler label.
Thanks for the contribution. I had to change it so that the sampleLabel is only changed if the sampler does not set the label, as both the existing samplers (SleepTest, JavaTest) do this.
This issue has been migrated to GitHub: https://github.com/apache/jmeter/issues/1786