Whatever the problem there are a number of ways to get aroud it, but why were the mercuric oxide cells discontinued anyway? The story punted around in UK was somethong to do with the disposal of the battery and the contamination it would cause if they continued to be used and disposed of in a careless way.
Can I suggest that is a load of old rubbish! All the fluorecent tubes that are used in the world all have a certain percentage of the content of the tube linings derived from Mercury so what happens to them when they expire. Usually they get thrown into a bin to be recycled (at least in UK). They are gradually being phased out but on the grounds that LED is more efficient, not safer!
Why can't 1.35v mercury batteries returned for use. The quantity of mercury which would cause problem is almost certainly at the bottom of the pile when you think of the damage that all other types of contamination is proven to cause. Smoking, vehicle exhaust fumes, CO2 discharge, plastic irresponsibly discarded, I could go on, the list could be almost endless.
Now, many years after the dicontinuation of the sale of mercury batteries and the total absence of new cameras that use a mercury cell surely there is a good reason to offer a limited production just to keep these photographic gems working properly. After all, mercury cells last a lot longer than a Wein cell, they were cheaper, and they were 100% reliable. You could be using a camera with a Wein cell one day and the very next after only a few months it is dead! Mercury ones lasted many years if only used to power the meter.
As we should all now know of the possible dangers, we as photographers who value our equipment should be trusted to act responsibly. How about, a system where if you had one already, you could not get another unless you returned the discharged one. Yes, OK, I'm tilting at windmills, but a blanket ban, is it really necessary - is it? I would suggest NO!