Experience in stability WSPR

What happens to the decoding signal, with QSB?
The essence of the experiment:
Turn on the receiver in the given time and look at the WSPR decoding.
1) Receive for 1:30, 1:00 (full signal around 1:50). Decoded! :woohoo:
2) Receive for 0:30. Does not decode.
3) Receive within 1 minute, shifted relative to the start signal for 30 seconds, i.e. from 0:30 to 1:30. Decoded!
In the picture a visible signal (1:50; abbreviated: 1:30, 1:00, 0:30; 1:00 with an offset).
The result:
Adopted by half of the WSPR signal already provides decoding of the message!

Image icon WSPR-obryv.PNG122.24 KB