What is the controversy/issue surrounding Jerusalem as Israel's capital? I was reading this article where representatives at the 2012 Democratic National Convention booed in disagreement over a platform position regarding Jerusalem as the capital of Israel.

I'm not interested in a political debate in asking this question; rather I am interested in what is the thought process behind the position that would contest Jerusalem as Israel's capital?
This issue isn't really anything to do with Christianity, although it's an issue which Christians sometimes take sides on.

When the State of Israel was created in 1947-48 Jerusalem was given a special status, not a part of Israel proper:  "The City of Jerusalem shall be established as a corpus separatum under a special international regime and shall be administered by the United Nations." The Israeli capital was established as Tel Aviv

Israel took effective control of West Jerusalem in 1948 and the rest of it in 1967, and has retained it ever since, declaring it to be their capital. Many nations, including until now the US, retain their diplomatic missions in Tel Aviv and consider it to be the capital, avoiding the implied recognition of the legitimacy of Israel's control over Jerusalem.

See: http://en.wikipedia.org/wiki/Positions_on_Jerusalem