Matlab or fitensemble strange behaviour!

Hello, I am having this strange behaviour that I am trying to justify for more than a day now. Changing the value of an unused variable affects the results. Here is a snippet of the code:

a=Some vector
Number=50
     mu=mean(a);
     stds=std(a);
     Covar=cov(a);
     z=zeros(Number,100);
     for ii=1:Number
         z(ii,:)=mvnrnd(mu,Covar);
     end

model =fitensemble(bagging classification);

My model changes if I change the variable Number! What's going on? Is it possible that changing Number is somehow affecting fitensemble initialization? Also, when a specific Number is used, then the model is consistent whenever that Number is used!

EDIT: Here is a working code. In my original code a and b are some data, but using randn could replicate the problem. Please notice that if Number is changed, the model is changed. Roughly, sum(model.UseObsForLearner(:)) changes accordingly.

rng(5)
temp=randn(100,200);
a=temp(1:50,:);
b=temp(51:end,:);

Number=10

       means=mean(a);
       stds=std(a);
       mu=means;
       Covar=cov(a);
       z1=zeros(Number,200);
       for ii=1:Number
           z1(ii,:)=mvnrnd(mu,Covar);
       end
  classLabels=[ones(size(a,1),1);-1*ones(1*size(a,1),1)];
  model =fitensemble([a;b],classLabels,'bag',50,'tree','type','classification');

sum(model.UseObsForLearner(:))

Many thanks

EDIT 2: I am getting closer. It has something to do with bagging. When I change from bagging to GentleBoost, the result is consistent and is not affected by the variable Number.

[Jan]

Please post the original code. A rough paraphrased pseudo-code might reveal the actual problem, because you show us your intention - but the problem is, that the code does not do what you expect. If the code conatins a cause for a "strange" behavior, this detail is concealed yet.

[Louis]

Thank you, Jan. I updated the code. This is a working code that replicates the problem.