'circ' argument to ezsurf not working

[Ben Sunshine-Hill]

Per the docs, it seems like appending the argument 'circ' to ezsurf, ezmesh, etc. should restrict the plotting domain to a circle within the bounds. But trying to use it produces the following error:

octave:5> ezsurf('x*x-y*y', 'circ')

error: `fstrx' undefined near line 333 column 46

error: evaluating argument list element number 1

error: evaluating argument list element number 1

error: evaluating argument list element number 1

error: called from:

error:   C:\Octave\Octave3.6.1_gcc4.6.2\share\octave\3.6.1\m\plot\private\__ezplot__.m at line 333, column 11

error:   C:\Octave\Octave3.6.1_gcc4.6.2\share\octave\3.6.1\m\plot\ezsurf.m at line 73, column 19

octave:5>

This is Octave 3.6.1, i686-pc-mingw32. The prebuilt binaries, with the octaveforge packages installed.

Anything I'm doing wrong?

Ben