Why do they knock off the mov 5 buff? Working as intended?

Speed shrines may be triggering an "In combat" effect which removes the +mobility bonus you get from them. Just a thought.

Can you provide evidence to support this?

If this is true, wearing boots 2 should give you the same speed number as wearing boots 5 on a speed shrine.

If anyone can confirm this to be true or not true, feel free to post it up (I'm at work now and can't test).

I already explained it, I tested it with a friend without boots, with boots 1, and with mobility. it doesnt put you in combat. it does exactly what I said above.

create a custom game, select crystal scar and test it.. how hard can it be ?

Or just look it up. Speed over 415 is reduced by 20%, speed over 490 is reduced by 50%. You're still faster, you just don't get as much bonus.