"Strange behaviour: struct with cell values"
The STRUCT() documentation explains what happens with cell array inputs: "... if value is a scalar cell array, then s is a scalar structure... If value is a nonscalar cell array, then s is a structure array with the same dimensions as value."
So it is very simple: if you want the output to be a scalar structure, then the input must be a scalar cell array.
You can achieve this very easily by nesting your (non-scalar) cell array in a scalar cell array:
order = 1; %Dumm
param = {1,2,zeros(2,2)};
opt2 = struct('order',order,'param',{param})
