How to deallocate memory of mathematica.exe

Question

First

r[t_] = {10 Cos[3/2 π t], 10 Sin[3/2 π t] + 3 Cos[6 t], 3 (1 - Cos[5/2 π t]) + 1};

Next, when I evaluate these lines, the memory reserved by mathematica.exe increases by 110 mb.

Graphics3D[{CapForm[None], Tube[FirstCase[ParametricPlot3D[r[t], {t, 0, 1}],
  Line[___], 0, {0, ∞}], 1/8]}, PlotRange -> {{-20, 20}, {-15, 15}, {0, 15}},
    Axes -> True, Boxed -> False, AxesOrigin -> {-20, -15, 0}]

Everytime something is changed in the plot I reevaluate the code, and then the previous plot is gone. However, the memory isn't freed, and eventually there is no more memory. Exit doesn't work because the memory is reserved by mathematica.exe. I also tried $HistoryLength = 0 which doesn't make a noteworthy difference.

How to free this memory without terminating mathematica.exe?

Edit: When leaving out CapForm[None] then MemoryInUse[$FrontEnd] is as good as constant. So this is a probably just a bug of CapForm.