C# is loading Outdated File

i have a curious Problem...

I try to read a File with:

StreamReader r = new StreamReader("Content//spriteShader.fx");

It's a simple HLSL Shader File.

So i write "return float4(1,0,1,1);" in the .fx file. I compile, run, everything is output well in the Console.

Now i change the .fx file to "return float4(1,1,1,1);" i save and run the Program but the Output is still the old one "return float4(1,0,1,1);"!

I look in the Build Folder an here i see ne newer File!

So my Question is: why Streamreader is loading the Outdated File when in the Build folder is always the newer file ( this work!).

The Solution is a Class Library not a Windows Application if this helps. Anybody have an idea?

EDIT: when i make a space in the .cs file or another change and save the .cs File again, the newer file is loading!

BuildAction: Compile Copy: Do not copy ( when i switch to Copy Always the problem is the same )