ConnectX-3 40GbE with Mellanox QSFP DACs to a Dell PowerConnect 8164: link comes up briefly then stays down

A Mellanox ConnectX-3 40GbE NIC connected with Mellanox QSFP passive copper cables (MC2210126-005) to a Dell PowerConnect 8164 (firmware 5.1.4.5) produced a link-up event for a few seconds followed by a permanent link-down. The same cables worked NIC-to-NIC, and Dell refused support because the cables were untested with their switches. Another user reported the same on a PowerConnect 8024F (Dell SFP+ cables only) and on a Brocade 8000.

• Hardware: Mellanox ConnectX-3 40GbE, Dell PowerConnect 8164, Dell PowerConnect 8024F, Brocade 8000
• Transceivers: Mellanox MC2210126-005 QSFP+ DAC
• Form factor: QSFP+, DAC

Symptoms / messages:

link up for a few seconds then down
switch vendor refuses untested cables