I think I found a small cosmetic glitch in TeamCity 9.0.2. One build failed, so the green markers of the project, the build configuration, and the build itself turned red, which is fine. Now I committed the fix to VCS, so the next build in TeamCity succeeded. Now the red markers of the build configuration and the last build turned green again. However, the marker of the project stayed red. Only when I reload the project overview page all markers are shown green again.
I have attached a screenshot of the issue: