Center parameter interpolation

I was hoping that switching the center parameter's keys to smooth interpolation would result in a smooth change of direction in a zoom animation. A gentle, natural-looking curve instead of an abrupt turn-on-a-dime. But the interpolation settings don’t seem to have any effect. It's always the same sharp turn halfway through.

Smooth interpolation:

Linear interpolation:

No interpolation:

Hi Eric,

I'm sorry for the late response! I find this very curious as well. Can you share the parameter set so I can have a look myself?

Thanks Frederik.

01MiddleKeyCenterSmooth {
fractal:
  title="01 middle key center smooth" width=640 height=180 layers=1
  antialiasing=yes
layer:
  caption="Background" opacity=100
mapping:
  center="-0.5/0@#0SS-1.96961505275/-0.0012317513@#7840NN0.6/-0.03@#15\
  840" magn="1@#0LL1.9791062@#7840LL4@#15840E"
formula:
  maxiter=100 filename="Standard.ufm" entry="Mandelbrot" p_start=0/0
  p_power=2/0 p_bailout=4
inside:
  transfer=none
outside:
  transfer=linear
gradient:
  smooth=yes index=0 color=8716288 index=100 color=16121855 index=200
  color=46591 index=300 color=156
opacity:
  smooth=no index=0 opacity=255
}

02MiddleKeyCenterLinear {
fractal:
  title="02 middle key center linear" width=640 height=180 layers=1
  antialiasing=yes
layer:
  caption="Background" opacity=100
mapping:
  center="-0.5/0@#0SL-1.96961505275/-0.0012317513@#7840LL0.6/-0.03@#15\
  840" magn="1@#0LL1.9791062@#7840LL4@#15840E"
formula:
  maxiter=100 filename="Standard.ufm" entry="Mandelbrot" p_start=0/0
  p_power=2/0 p_bailout=4
inside:
  transfer=none
outside:
  transfer=linear
gradient:
  smooth=yes index=0 color=8716288 index=100 color=16121855 index=200
  color=46591 index=300 color=156
opacity:
  smooth=no index=0 opacity=255
}

03MiddleKeyCenterNone {
fractal:
  title="03 middle key center none" width=640 height=180 layers=1
  antialiasing=yes
layer:
  caption="Background" opacity=100
mapping:
  center="-0.5/0@#0NN-1.96961505275/-0.0012317513@#7840SL0.6/-0.03@#15\
  840" magn="1@#0LL1.9791062@#7840LL4@#15840E"
formula:
  maxiter=100 filename="Standard.ufm" entry="Mandelbrot" p_start=0/0
  p_power=2/0 p_bailout=4
inside:
  transfer=none
outside:
  transfer=linear
gradient:
  smooth=yes index=0 color=8716288 index=100 color=16121855 index=200
  color=46591 index=300 color=156
opacity:
  smooth=no index=0 opacity=255
}