apt-get update and source behavior

[dan@cg619985-a.adubn1.nj.home.com]

Have a question concerning apt-get update. If I grab a source package, let's sayit be libc6. Compile it, install it. Then, when I do an apt-get update, even though there was no update of this package on the server, it will still download a binary version and overwrite my just compiled glibc with exact same version number.
My question is, how would one configure apt-get, or make it hold back some packages on upgrade, or how to fool it, so that it does not overwrite compiled packages with binaries when doing apt-get update? If you can give a specific solution,or point to some documentation, would be of great help. Thanks.