Ports which adhere to the old IEEE 1394:1995 specification are electrically more prone to damage during hotplugging than later 1394a:2000 hardware. And the 4-pin iLink ports are mechanically not very reliable. Damaged 6-pin 1394a ports or 9-pin 1394b ports on the other hand are not very common but do occasionally happen.
> Will try older Ubuntu later.
If you have the opportunity, please do so. A driver regression is unlikely to be the cause of this problem but it would be good if you could test with older firewire-ohci + firewire-core kernel drivers, or ideally with the ohci1394 + ieee1394 + raw1394 kernel drivers of kernel 2.6.36 or older to be sure.
> I suppose this points to defect HW?
Yes.
> How easy are these things to break?
Ports which adhere to the old IEEE 1394:1995 specification are electrically more prone to damage during hotplugging than later 1394a:2000 hardware. And the 4-pin iLink ports are mechanically not very reliable. Damaged 6-pin 1394a ports or 9-pin 1394b ports on the other hand are not very common but do occasionally happen.
> Will try older Ubuntu later.
If you have the opportunity, please do so. A driver regression is unlikely to be the cause of this problem but it would be good if you could test with older firewire-ohci + firewire-core kernel drivers, or ideally with the ohci1394 + ieee1394 + raw1394 kernel drivers of kernel 2.6.36 or older to be sure.