Maxima tries to display things of the form x-y so that there is no leading
negative sign. As far as Maxima's display routines are concerned, %i is just
another expression (nothing special about it), and it does the same thing to
expressions involving %i.
To turn off this display trick, set negsumdispflag:false.
This will now consistently display complex constants as nnn*%i+mmm. Not the
order you prefer, but at least it's consistent.
I don't know of any simple way to force display as mmm+nnn*%i.
-s