I have found that it is impossible to regenerate the system maintenance > self-signed certificate on the 2860 running the latest available firmware.

You can get to the screen and enter the information for the new certificate but when you press on the generate button nothing happens. I do not see the normal popup warning that this will take several minutes.

Repeated the same action on a 2862 running the latest firmware and it works fine.

I have found this reported as a bug on the 2862 that was fixed in the .1 release of its firmware.

Is this bug? Is there a workaround?

I've noticed the same problem.