let me put it real simple - you guys are too smart for your own good you over intellectualize everything
Let me put it simpler. Your wrong.
has anyone ever been watching cgminer when the pool goes hay wire (happens a lot with pools that pool hop or share selling service) and all of the sudden that 5870 that was just humming along nicely went from showing 435.5/429.3MH/s is now showing 730.3/239.2MH/s and no shares are getting through at all? ok yeah its all a function of mhash it will even out eventually but right now in that moment the only thing I care about is am I making money? because obviously the fact that now my 5870 is magically giving me 700 mhash on a single thread its costing me money and not making me any (no shares = no money)
Couple points:
1) If a pool going haywire retroactively changes your avg since start well you got a lot bigger problems. The second number is hashrate since start it is # of hashes / elapsed time. So after 20-30 min in it shouldn't change significantly within a few seconds.
2) That has nothing to do with intensity. If you change intensity it will change mhashes. It will also change shares BUT shares rate ("U:") has roughly 4 magnitudes more variance for a given time period.
So looking at share rate in the short term may mean you are simply looking at noise.For example
start cgminer -let it run 2 minutes check U rate.
now stop cgminer
fart, yes far.
start cgminer -let it run 2 minutes check U rate.
Tada farting must affect share rate. It is entirely possible the two values will differ by 20% or more. Farting (or lack of farting) boosts share rates 20%!
So you seeing a major change in share rate doesn't mean anything unless you are waiting a very very very long time. Share rate (U) really only stabilizes after 10K or so shares. I would say 20K to 50K would be better. So unless you are setting intensity and waiting half a day to make sure the results are valid using share rate in the short term is useless.
Of course none of this has anything to do with your original claim.If you change intensity you should see a change in MH/s. Period. If you aren't then something is wrong. If a pool goes offline and that retroactively changes your prior MH/s average (yes the second # is the average since starting) then something is wrong. You shouldn't rely on your conclusions for anything.