Please, do not change this behavior. A lot of custom maps have things based on this. It's been this way since the beginning, and if mappers (if they cared/needed) fixed it in their maps.
True, this "bug" is very used in modern gameplay and is a part of set "thing you should know" which extends learning curve and makes GoldSouce games more interesting.
As explained above, this feature is needed for certain maps, changing it now would break a lot of existing content.
Nothing extracted yet.
In GoldSrc players can activate buttons through walls. In Source this bug is already fixed.
I did a test map: https://dl.dropbox.com/u/72298737/func_button-test.bsp