Problem with Probe Signal Vector Block

Hi,

I made a Flowgraph in GNU Radio which shows me the FFT of the samples
that are sent by a Raspberry Pi over TCP. It looks like this:

Osmosdr Source -> Stream to Vector -> FFT -> Complex to Mag -> Log10 ->
Vector to Stream -> Moving Average -> Stream to Vector -> Probe Signal
Vector

I want to save the values of the FFT in a list in my Python program
later. Now what I tried to do was to plot the probed vector with
Matplotlib. I also replaced the last Stream to Vector Block and the
Probe Block with a QT Time Sink to control the output. But the picture I
get with Matplotlib is totally different. So my question is if this is a
problem of how to do the probes on the signal vector or if it could be a
problem of Matplotlib.

Thank you in advance!