This is not a problem with the "parent" property, but rather a general difference between how Octave and Matlab handle property/value pairs.  In Octave, prop/val pairs apply to the nearest XY data and you can have different prop/val pairs for different sets of XY data.  In Matlab, you can specify a LineSpec per XY data set, but ALL XY data share the prop/val pairs.

Example

x = linspace(-2*pi,2*pi);
y1 = sin(x);
y2 = cos(x);
plot (x,y1,x,y2, 'color', 'm')

The result is that the first line uses the default color from the ColorOrder property while the second line has the default overridden to magenta.

File:octave.png

In Octave, you can apply properties individually so this works

plot (x,y1, 'color', 'r', x,y2, 'color', 'm')

File:octave2.png

If you try this syntax with Matlab it will generate an error because it only allows one set of property/value pairs and it must occur after all XY data has been specified.