Session based digital I/O using the DAQ toolbox fills memory

Dear all

I'm trying to send a PWM signal to a motor using the DAQ toolbox in connection with a NI USB-6251 card and the sessin based interface. I add an event listener which does continuously output the signal in the background. For some reason, the memory of my PC is filled up withing roughly a minute (64-bit, Win7, Matlab R2013a). Interestingly, the memory is not freed when issuing clear all or clear functions. Leakage?

Can anyone give me a reason for this and a workaround? Is there a better/more elegant option to produce a PWM with the existing setup?

Here is the code I'm using

clear all; close all; clc
%%init

clockFreq = 10e6;

sClk = daq.createSession('ni');
sClk.addCounterOutputChannel('Dev1','ctr0','PulseGeneration');
sClk.Channels(1).Frequency=clockFreq;
clkTerminal = sClk.Channels(1).Terminal;
sClk.IsContinuous = true;
sClk.startBackground;

s = daq.createSession('ni');
s.addDigitalChannel('Dev1','Port0/Line2','OutputOnly');
s.Rate = clockFreq;
s.addClockConnection('External',['Dev1/' clkTerminal],'ScanClock');

%%Output PWM signal
freq=158000;
Ns=round(clockFreq/freq);
freq=10e6/Ns;

duty=0.5;

L1=floor(duty*Ns);
L2=ceil((1-duty)*Ns);

outputData(:,1)=[ones(L1,1);zeros(L2,1)];
outputData=repmat(outputData,round(2*freq),1);
s.IsContinuous=true;
s.queueOutputData(outputData);

lh=s.addlistener('DataRequired', @(src, event) s.queueOutputData(outputData));

s.startBackground();
pause

%%clean up
s.stop;
s.IsContinuous=false;
s.queueOutputData(0);
s.startForeground();

delete(lh)

Any help is appreciated.

Philipp