W5100 Sometimes Won't Connect After FW Upload

I've had persistent problems with W5100s not connecting to the network, most often immediately following a FW upload. It's not the specific hardware, as I've seen the behavior on more than a dozen different systems, and with completely different firmwares. Sometimes, I can get it working again by doing multiple restarts (i.e. - toggling DTR on the Serial device), but even that is not 100% reliable. At times, the only thing that gets it working again is to power everything down, and back up again. When it gets into this state, it appears to be completely oblivious to the presence of a network, as there is only a single red LED lit on the W5100 board, with no indication of any attempts at communication whatsoever - not so much as a single blink on any of the other LEDs.

Is anyone aware of any problems with the W5100 that would explain this, or any FW work-arounds to make it more reliable?

Regards,
Ray L.