At an early stage of the processing, false detections due to diffraction spikes on the PSF, etc, were present around bright stars. They were considered as new sources, not being part of the Initial Gaia Source List (IGSL). Thanks to a dedicated cleaning,Figure 10.8 shows that the artefacts present at an early stage of the Gaia DR2 processing seem no more present in Gaia DR2.
We had developed tests to detect automatically non random features. They actually found real structures (e.g., a dark cloud near HIP 27406, Figure 10.9) rather than artefacts.