Discrete Time Integrator Trouble

I am using a discrete time integrator in Simulink and am getting very strange results. I am squaring a waveform from my USRP radio such that all values received by the discrete time integrator are positive yet the result of the integration doesn't always go up (sometimes it is goes down, though, the trend is to go up). I don't see how the output of the discrete time integrator could ever go down when its input is always positive.

[MATLAB_User]

Comments: I found that if I 'unbuffer' the date being sent to the discrete time integrator it seems to work. It must have been operating on the whole block. Why the discrete time integrator can't operate on a block of data I don't know.