bubble plot: surface versus diameter

[John Denker <jsd av8n com>]

Example file:
  http://www.av8n.com/physics/bugs/bubble-diameter-area.gnumeric

For this plot, under properties -> graph -> chart -> plotbubble1
there is an option to size the bubbles according to "surface" or
"diameter".  It appears that both are checked by default (or
maybe neither) ... and I cannot check or uncheck either one.

Observed result:  Apparently, all bubbles are plotted by surface area.

Desired result:  According to the documentation, usedrs should be 
allowed to choose.
   https://projects.gnome.org/gnumeric/doc/sect-graphs-elementProperties-plots.shtml

Priority:  Not urgent, because there is a workaround.

Workaround:  Users can prescale their data.

 uname -a
Linux asclepias 2.6.39.4 #4 SMP Thu May 30 01:02:55 MST 2013 x86_64 x86_64 x86_64 GNU/Linux

 gnumeric --version
gnumeric version '1.12.1'
datadir := '/usr/share/gnumeric/1.12.1'
libdir := '/usr/lib/gnumeric/1.12.1'