See attached screenshots.
Maybe related to the Sliders window? Because it only seems to happen on the bottom part of the grid and I cannot reproduce on smaller Grids (ie 10x10).
Can reproduce systematically on .494 x64, on Win10pro, tested with Nvidia and Intel graphics, 1920x1080 with 125% Scaling.
If I lower screen resolution or lower the window scaling, I cannot reproduce.
Noticed this when testing beta .494, don't know if it was present before.
There is also a bit of "jittering" when deselecting the source.