Lucky ADS-B Reception?

I have several ADS-B receivers running at the moment, 3 Raspberry Pi boards using DVB-T SDR dongles. When checking on of the receivers I saw there was a black stripe in the reception pattern. It was pointing east and could mean I received a real long distance position, about 325 NM or about 600 Km.

ADS-B 325 Nautical Mile Reception
ADS-B 325 Nautical Mile Reception

The antenna used is a collinear dipole like in the picture below. Very simple antenna but also very effective. The antenna is at about 7,5 meter in the house at the top floor.

ADS-B Collinear Dipole Antenna
ADS-B Collinear Dipole Antenna