In some scenarios the RTT Clear optimization can produce artifacts on screen. This can be checked ex. by running RenderPerfTest CircleBlend* tests using a small object count (in my case n = 10 is sufficient). Disabling the optimization fixes the artifacts.

Artifacts can also happen in other cases where some form of blending is used - see openjfx-dev thread https://mail.openjdk.org/pipermail/openjfx-dev/2025-December/057961.html