tshark: incomplete probe request packets on raspberry pi

Hi all,

I'm running the following tshark scan to get MAC/SSID/signal dbm from probe requests:

sudo tshark -I -i wlan0 -T fields -e wlan.sa_resolved -e wlan_mgt.ssid -e radiotap.dbm_antsignal type mgt subtype probe-req

On a Raspberry Pi. The results are nearly always partial packets, generally just the signal dbm and occasionally an SSID, but pretty much never a MAC address. When I run the same scan on my Macbook Pro in the same room, it generates all three fields for every result. I assumed this was a weaker wifi adaptor on the Pi, so I bought a Linksys AE3000 adaptor (and a couple of others to test), and got the same results. Have tried running the adaptor from a powered USB hub, same result. The Pi is running from a power supply, not battery. Anyone experienced the same thing, or have thoughts on why this is?