In 1994, Mitt Romney Called for Ted Kennedy to Release All His Tax Returns:
And thus, the circle of life is complete:
From the Hotline, April 15, 1994, quoting a Boston Globe article from April 14, 1994:
"With the tax-filing deadline looming," businessman Mitt Romney (R) challenged Sen. Edward Kennedy (D) to "disclose his state and federal taxes to prove he has 'nothing to hide,'" but businessman [and primary challenger] John Lakian (R) "called Romney's move 'bush league.'" 

Romney: "It's time the biggest-taxing senator in Washington shows the people of Massachusetts how much he pays in taxes."   

Romney"said he would disclose his own state and federal taxes for the last three years 'on the very day that Kennedy turns over his taxes for public scrutiny.'"  Kennedy aides "said ... they could not immediately respond to the Romney challenge."  Kennedy "does not release federal disclosure forms every year, but those have only ranges for income and investments.  The forms indicate he receives hundreds of thousands of dollars in income from blind trusts and other family wealth."  Romney "chided Kennedy for never releasing his state or federal taxes in the 32 years he has served in the Senate." 

Maybe it only counts for state races, not national ones, no?

Update: CNN and the Washington Post had this a couple of days ago, but it's gotten surprisingly little play. 

Update 2: Debating Kennedy in 1994, Romney complained that he wanted to talk about the issues when Kennedy aired ads about Bain.  Man, he won't ever talk about Bain unless it's unmitigated praise for it.

Update 3 (This is getting positively Greenwaldian): In 2002, Romney flip-flopped on the need to see the taxes of his opponent. He said that he was wrong and that now he values privacy.