Soldiers lying in gras should slide under the ground. Sadly this system doesnt work good enough because the soldiers begin to slide into the ground at too big ranges.

Before they slide under the ground the gras allready begins to disappear leaving them on a plain field for a large amount of distance.

Here is a zip with some screenshots of the bug.

You can see how the soldiers should be hidden by gras but since the gras allready begins to disappear and they yet not begin to slide under the ground - they become far too well visible.
https://dl.dropboxusercontent.com/u/4934308/Arma%203/gras_bug.rar