Integer timeline step length confusion

As of dbe0ac66, if I set both dt_min and dt_max to 1e-8, and timeEnd to 1e-7 then we calculate a timeBase of 3.725290e-16. However, we use a step length which is much smaller than the minimum:

engine_init: Absolute minimal timestep size: 3.725290e-16
    Step #         Time    Time-step  # Updates Wall-clock (ms)
         0 0.000000e+00 0.000000e+00          0           0.000
         1 6.250000e-09 6.250000e-09    1841127        2370.150
[ ... a bunch of steps of the same length  ... ]
        16 1.000000e-07 6.250000e-09    1841127        2364.122
main: done. Bye.

I'd expect a step length of the nearest multiple of 3.725290e-16 to 1e-8. Am I wrong?

I see similar behaviour whether I use swift or swift_fixdt.

If I increase dt_max to be greater than timeEnd, then we appear to get stuck in ````runner_dokick. If I then increase timeEnd``` (so ```dt_min``` is 1e-8, ```dt_max``` is 1e-6 and ```timeEnd``` is 1e-5) then I see a regular pattern of step lengths before it gets stuck with a zero-length step at t=```timeEnd```:

    Step #         Time    Time-step  # Updates Wall-clock (ms)
       260 9.414062e-06 3.906250e-08    1837561        2376.584
       261 9.453125e-06 3.906250e-08         54          65.733
       262 9.492187e-06 3.906250e-08        104          53.476
[ ... a bunch of steps of the same length  ... ]
       274 9.960937e-06 3.906250e-08        474          59.235
       275 9.980468e-06 1.953125e-08        172          64.479
       276 1.000000e-05 1.953125e-08          2          58.446
       277 1.000000e-05 0.000000e+00    1837562        2372.388

There are up to three different issues here, but I'd guess they're closely related.