@Lee, I have a comment for you at the end of this post.
Here is what is happening with my real-time editor for grass. I divided it up into 4 videos. It was easier for my brain to separate what is going on.
The first video shows the map editor and where I grow some grass. After so doing I run the test game and go into the real-time editor. I want to delete (shift-LBM) a small swath of grass through the grass that was made. The first thing you notice is that the grass being deleted is way larger than the brush. It seems to ignore the brush size and deletes the same area.
This next video clip shows the map editor after deleting some grass. It does seem to show a smaller amount deleted but when you go back into the real-time mode you hardly notice any deleted grass. So, then time I decided to delete a whole bunch of grass.
In the 3rd video clip, you will see the map editor showing that hardly any grass was deleted and a strange depiction of what it thinks. I then went to the left end of the grass patch and added some grass (LMB). As you can see it doesn't show any grass being added in real-time.
In the final 4th video, you will see the map editor showing that there was some grass added. Going into real-time there is actual grass there and then I went into the area that I supposedly delete all of that grass and you will see that it is somewhat thinned out when it should all be gone.
Ooops! Wrong video. Here's the right one.
@Lee, Now, because there are some people who are not experiencing this issue I really don't have a guess as to what is wrong in the engine code. You will see what my specs are for the hardware environment. It is an Alien gaming machine with a video card that might have something to do with it. ??? But I don't know what that could be. I did delete/uninstall GG and re-installed on a different drive. It did not make any difference. So I brought back to the C: drive which is faster.
Alienware Aurora R7 with SSD 256GB boot drive ( C: ) and a secondary drive ( D: ) that is 2TB
Intel(R) Core(TM) i7-8700 CPU @ 3.20GHz 3.19 with Intel Turbo-burst
Installed RAM 16.0 GB
64-bit operating system, x64-based processor
Windows 10 Home
NVIDIA GeForce GTX 1070 with 8192 MB GDDR5 and 8095 MB shared system memory