Mathematically 5 is the same as 5+0i, so the output is correct.
So omitting the imaginary part is a question of taste.
If you want to display it, do this expliticitly:
x = 1 + 2i;
sprintf('%g %gi', real(x), imag(x))
Alternatively you can copy the code of mat2str to e.g. mat2stri anywhere in your user-defined folders in the path and remove the line:
imagStr(imagVal == 0) = "";
