Yes and no, it was resolved but the issue showed up again

Great tip, exactly what I need though I don't know how to use it quite :/
If I double click a line it opens a page where it says No Source Found.
Here is a screenshot on the callstack on a breakpoint at the opening bracket of the DoWork the second time it is run:
http://s246.photobucket.com/albums/g...krmklipp-2.png

This is how the program misbehaves:

I start the worker
The DoWork is run
The RunWorkerCompleted runs

Now, if I don't close the program and continue this happens:

I start the worker
The DoWork runs
The DoWork runs again
The RunWorkercompleted runs
The RunWorkercompleted runs again

If I continue even further:

I start the worker
The DoWork runs
The DoWork runs again
The DoWork runs again!
The RunWorkercompleted runs
The RunWorkercompleted runs again
The RunWorkercompleted runs again!

And so on, one more time for each thing each time I repeat...weird!
I have written an own class for managing the backgroundworker, I can write it here if you want. I have breakpointed the only worker.RunWorkerAsync() and it only executes the first time when I want, the rest happens magically....