wlan0 RX Packets dropped

I have a new installation of “adsb-receiver_2.5.0_dump1090-mutability_raspbian-jessie-lite”, it works well but I have some questions.
I use a Pro Stick Plus, directly plugged into the raspberry pi 3.
First question:
When I have both eth0 and wlan0 connected (metrics are set correctly in favour of eth0) I see that most traffic passes wlan0 in stead of eth0 while I expect it to be otherwise.
Second question:
On the wlan0 interface I can see with ifconfig that a LOT of packages are lost on RX (about 50%).
What could cause this and does it effect the results?

Thank you!!

My stats here: flightaware.com/adsb/stats/user/rexxbr

Both questions are quite specific to the image that you are running, try the adsbreceiver forums?