Thanks Derek,
I had noticed this the other day and knew that it must be something that was built in to EE so looked through the change-logs and found it listed there. I only noticed it as I had just installed a new Dev install to test something out and I just left the standard template in there and this is when I saw it. I have another site running 1.6.1 but I never use the {stylesheet} path variable so figured out what was going on. I recognised the numbers immediately as I used to do this sort of thing in Flash many moons ago to refresh content. An old trick but always a good one! 
So the answer is that you can over-ride this by simply not using the {stylesheet} path variable although I may try using it from now on as it really is a neat feature! 
Best wishes,
Mark