The sources jar are not downloaded if the first download returned a 404. Scenario: I run idea task and the sources.jar were not in my repo at the time, then I added the sources, and re-run the idea task to no-avail, the sources.jar files were never downloaded. I tried -C rebuild, --refresh dependencies but the only think that works was the nuclear option: Drop the cache folder of gradle!
Thanks for the report: I can confirm that this is indeed not working as expected. The sources are actually being downloaded, but for some reason the generated IDE files are not being updated.
I’ve raised GRADLE-2206 to track this.