Why does my minecraft seed change when I enter one?

Okay, so I like to play minecraft and when I find really cool seeds I enter it in and create the world for pc. Well, when I get in the world, I check to see what the seed is and it is a totally different seed than what I entered. Can someone tell me why? It is really annoying.

Why is this? Well world generation code gets modified over time. Like the seed gargamel. Check it in 1.7.3 and then in 1.8.1, it's totally different.