gfactor -> Polynomial quotient is not exact

hello,

using Maxima 5.29.1,
from

f: 
v0*(1+sqrt(5)*l*sqrt((x1-x2)^2+(y1-y2)^2+(z1-z2)^2)+5/3*l^2*((x1-x2)^2+(y1-y2)^2+(z1-z2)^2))*exp(-sqrt(5)*l*sqrt((x1-x2)^2+(y1-y2)^2+(z1-z2)^2));
g: 1/v0*exp(sqrt(5)*l*sqrt((x1-x2)^2+(y1-y2)^2+(z1-z2)^2));
diff(f, x2, 2);
multthru(g,%);
xthru(%);
subst(r2, (z1-z2)^2+(y1-y2)^2+(x1-x2)^2, %);
subst(r, sqrt(r2), %);
subst(dx, x1-x2, %);
subst(dy, y1-y2, %);
subst(dz, z1-z2, %);
gfactor(%);

I get

Polynomial quotient is not exact
  -- an error. To debug this try: debugmode(true);

from what I found on the net,
it is a bug; my question is:
is there a workaround for it ?

thanks !

regards,
Laurent