Problem with passing Optional Arguements as a structure.

I'm having problems with using optional arguments as a structure. At the bottom, I've included the relevant portions of a function. I use this function as a subfunction from two different master functions. In one case it works fine, in the other I get errors that look like

Error using plot_edot (line 35) Argument 'LineWidth' failed validation with error: Expected input to be one of these types:

 _ double, single, uint8, uint16, uint32, uint64, int8, int16, int32, int64_

Instead its type was struct.

The problem is not actually with the Linewidth arguement, as the Linewidth value is assigned with identical code in the two master functions and I can change which argument is reported as having a problem by changing the order of the p.addOptional commands.

Clearly, there is something wrong in how I'm handling the structure in this routine, but I can't see it. Hopefully someone more experienced can tell me what I'm missing.

Raph

function [axis_id] = plot_edot (edot, time, varargin)
%--------------------------------------------------------------------------
%[] = plot_mass_fraction (nuc_name, edot, time, ...) 
% Plots mass fractions vs. time for provided data. 
% Inputs:  nuc_name: array of species names 
%          xmf: time dependent array of mass fractions 
%          time: array of times
%          SeparateLegend: draw separate legends for each lineset
%          LineStyle: line style of mass fraction lines
%          LineWidth: width of mass fraction lines
% Outputs: axis_id: handle of current axis
%--------------------------------------------------------------------------

% Create an instance of the inputParser class.
  p = inputParser;

% Define required inputs
  p.addRequired('edot',@(x)validateattributes(x, {'numeric'}, {'vector', ...
     'real'}));
  p.addRequired('time',@(x)validateattributes(x, {'numeric'}, {'vector', ...
    'real', '>=', 0}));

% Define optional inputs
  p.addOptional('LineWidth', 2, @(x)validateattributes(x, {'numeric'}, ...
    {'scalar', 'real', 'positive', '>=', 0.1, '<=', 10}))
  p.addOptional('LineStyle', '', @ischar)
  p.addOptional('LineColor', 'k',@ischar)
  p.addOptional('TimeFromEnd',false,@islogical)
  p.addOptional('TimeOffset', 0, @(x)validateattributes(x, {'numeric'}, ...
    {'scalar', 'real', 'positive'}))

% Parse and validate all input arguments.
  p.StructExpand = true;
  p.KeepUnmatched = true
  p.parse(edot, time, varargin{:})
  p.Results