sampleTerrainMostDetailed return wrong heights

Hi everyone!
image
The screenshot shows the problem i found, some sample points’s height higher that terrain surface, and some sample points’s height lower that terrain surface, anyone knows how to handle this?

Demo in sandcastle:

Before set Ground Translucency:


After set Ground Translucency:

Update:
I tried empty terrain, i have same height data as before, i’m confused how it works.


Thanks for the help