Maxima units problem?

gistfile1.txt

kill(all);
load("ezunits");

x : c1*t^2 + c2*t + c3$
dx : diff(x,t)$

eqns : [ev(x,t=0`s) = 0`m,
        ev(x,t=5`s) = 5`m,
        ev(dx,t=0`s) = 1`(m/s)]$

/*
  [c3 + 0 ` s  + 0 ` s = 0 ` m,
   c3 + 5 c2 ` s + 25 c1 ` s  = 5 ` m, 
                    m
   c2 + 0 ` s = 1 ` -]
                    s

In the first equation, c2 and c1 are missing, so their units don't end
  up contributing, and the resulting system is unsolvable. I think?
  */