PIC18 Ethernet module sent data invalid?

[E]

Hi wonderful EEVBlog community!

I'm struggling with the Ethernet module of a PIC18F66J60. I'm trying to get it to send data to my PC either directly or via a switch. Using the TCPIP stack demo app from Microchips MLA, I got it to compile and flashed it onto my self-designed board. I let it announce it's IP via UDP broadcast once every second, but when I sniff the network using wireshark I find no packets whatsoever.
The link and TX leds are showing the proper behaviour and I get the attached waveform on the TPOUT+/- pair. (yellow is TPOUT+, blue TPOUT- and purple is the difference). It shows the expected frequency of 10 MHz for this 10Base_T/Half-Duplex connection.

I don't know if this is what a ethernet waveform is supposed to look like and whether the levels are high enough.

Any ideas what could cause me to fail to find packets?

Btw: I tried both, static IP config and DHCP. The subnet mask, gateway etc. are set correctly, but I pick up *no* packets at all, no ARP, no ICMP, no DHCP, nada!
Edit: Waveforms are AC coupled, have a ~3V (VDD) offset.