I'm not very skilled with computers, but many of us have that problem with alpha-textures in SL. You know, when one alpha, that's supposed to be in the background overlaps another alpha, that's supposed to be in the foreground. Often happens with trees like here:
You see the palms of the background shining through the tree in the foreground?
Especially nekos know the problem very well, when they enter a danceclub and their tail vanishes, because the dancefloor is overlapping it.
To my knowledge, LL haven't found a solution for it. Prolly not even working on it. And I don't know, why it's not happening to all people. Kenshi for instance sees it all well. Maybe because he's using iMac?
Anyways... the only solution I found yet is to go to "Advanced" > "Rendering" > "Fast Alpha". Then the same picture looks like this:
When I check "Fast Alpha" I got some "halo" around some trees, but it's better then the disturbing overlappings.
If you have a better solution, let me know in comments!