Strange fill making problems

Hi experts,

i have a strange fill type in one object in a file a friend gave me. I noticed this only because i tried to print the file, but the object with the strange fill doesnt show up in the printing output.

While i'm used to the second picture (full black), this object has the first fill (There is this little box showing in it). Can someone explain what this is and how to get rid of it? The only solution i found is setting the fill color to "nothing" and then assign "black" again. Then the little box disappears.

Kind regards,

Jan Peter Lindner