Weird pixelated stripes on Textures

Hey all,
I imported a texture:

All was fine: but then i saved the texture:

Now if you zoom in, you can see weird looking stripes:

ATTACH=CONFIG]11506[/ATTACH]

You can see it better when the Red and Green Channel are deactivated:

This ‘bug’ is in my other textures too.
I think it’s the compression that made the pixelated stripes but I don’t know.

Can someone help me?
Many thanks in advance!

(PS: Sorry for my bad English, I’m from Germany)

Edit: Sorry,the last images position is wrong.It should be after ‘Now if you zoom in, you can see weird looking stripes:’