Question: Discontinuous Initial Conditions... Shouldn't Be?

So I am working on doing some trajectory simulations in Maple using standard Newton's Laws, some force expressions, and initial conditions.

Anyway, the numerical solution works fine if I let the initial conditions I specified (for z=-1) be actually for z=-0.9. To illustrate, when I give an initial condition like this:

x(-1) = x_0, D(x)(-1) = xd_0, Vz(-1) = v_0

the results don't make any sense. However, when using the same x_0, xd_0, and v_0 and I give initial conditions like this:

x(-.9) = x_0, D(x)(-.9) = xd_0, Vz(-0.9) = v_0,

the solutions at least make a bit of sense.

What's weird is that, when I let z -> 0.93 or so, the solution changes discontinuously. And this shouldn't happen. The initial conditions were calculated for and should work for z = -1. I don't understand why they aren't.

Here is my Maple document. ics1 are the problem.

dsolve_field_traject.mw

Do you guys have any idea what could be going on?