When there is a new firmware update for my Surface Pro, all good. Windows Update shows 'System Firmware Update' and the date '24/02/2016'. The size was a something megabytes. Installed ok.

But the question arises on subsequent runs of windows update. Every subsequent run shows the same update name and date but with a smaller size of 340kb. I can install it, but it will come back.

My guess is this is the correct behaviour and that this update is a ahem placeholder of some kind to report the current firmware version to the update process for some reason.

I have not investigated any further but it would be nice to know for sure that this is not an issue and any tech info about how this works : ).