I am trying to create a MATLAB class with a member variable that's being updated as a result of a method invocation, but when I try to change the property within the class it (apperently, from what I understood from MATLAB's memory management) creates a copy of the object and then modifies it, leaving the original object's property untouched. 

classdef testprop  
    properties  
        numRequests=0;  
    end  
    methods  
        function Request(this, val)  
            disp(val);  
            this.numRequests=this.numRequests+1;  
        end  
    end  
end  

 >> a=testprop;
>> a.Request(9);
>> a.Request(5);  
>> a.numRequests  

ans = 0  

Using a Vanilla Class 

When using vanilla class you need to tell Matlab to store a modified copy of the object to save the changes in the property value. So, 

>> a=testprop
>> a.Request(5); % will NOT change the value of a.numRequests.
5

>> a.Request(5) 
5

>> a.numRequests
ans = 
       0

>> a=a.Request; % However, this will work but as you it makes a copy of variable, a.
5

>> a=a.Request; 
5

>> a.numRequests
ans =
       2

Using the Handle Class 

If you inherit from the handle class, that is 

classdef testprop < handle 
then you can write, 

>> a.Request(5);
>> a.Request(5);
>> a.numRequests
ans = 
       2