The newer DB8E specs
https://www.antennasdirect.com/cmss_...s/DB8E-TDS.pdf show three lobes off the back side (see page 2 of 9) that could easily provide usable reception and/or pick up interference depending on the circumstance. Virtually all directional antennas will exhibit a pattern like this, though each will be unique in the number of lobes and relative gain.
I don't have the older DB8 specs, but would expect to see a similar ability to receive from the rear. I know of no directional antenna that can claim to block all reception from the rear. They simply concentrate the majority of their reception ability to the front.