Terrain Shadow causes vessel shadow to be visible in far distance
Apparently, enabled terrain shadows will create a shadow of your vessel which is visible in very far distances, in the case of Kerbin, the shadow starts to fade in/out ~90km ASL and becomes clearly visible ~85km ASL.
Barely visible at this altitude but it's already there:

Clearly visible at a slightly lower altitude:

The shadow also variate in size at different altitudes.
KSP: 1.7.0 Windows 64bit
Mods installed: Scatterer 0.0540
Reproduction steps: Enable terrain shadows (actually enabled by default), launch a vessel in daylight and keep an eye on the shadow. Disable the terrain shadow and launch another vessel, the shadow disappears around 2.5km ASL.
Log: output_log.zip
Known issue (at least for me). The reason is, by extending shadows to work at larger distances (what terrain shadows do), we also have to "spread" their precision over larger distances which makes them inherently blurry and less detailed. In this case the shadow of the ship which is probably one pixel on the shadowmap is being "spread". No workaround for now.