Sometimes the water surface doesn't like things beneath them

I like to do underwater images in GMod. But sometimes there are some minor graphical glitches. Here’s an example:
http://fav.me/daag0y1

As you can see in this image, the blue barrel is underwater and it should be look distorded by the water surface. It does but the barrel seems to be rendered twice. One time distorded and one time ignored by the water surface.

Is there any way to fix this with a command or is this a problem by some maps?

Try the dev branch.

I tried the dev branch but it’s the same, unfortunately. Do I have to change some cvars?

You are all out of luck then.