What I think is happening is the displayed hashrate gradually ramps up over 20 or 30 minutes until it plateaus.  I assume this is due to averaging.  However if your algo is switching frequently between coins, e.g. mona and vtc then you will see the displayed hashrates bob up and down without coming close to the local hashrate.  Again, I think this is just a function of the time averaging involved and it doesn't represent the actual hashrate at any given moment.

I wish there was a way of setting a delay before switching coins and even better if we could disable a particular coin from being switched to.