According to major ticket sales websites, Tony Leung and Eason Chan are scheduled hold a joint concert in Beijing...sometime. The Beijing News discovered that while one website, PiaoCN.com, gave the concert date as 28 May, another site, China Ticket Online, had it as 29 April. Although each site insisted its date was correct, the CTO site has since changed the date to 28 May.

A second peculiarity is that Tony Leung apparently doesn't realize he is scheduled to give a performance. And Eason Chan's manager said that they believed his performance to be part of a larger show with many artists, rather than just the two advertised.

Furthermore, as anyone who's tried to get Jay Zhou or Andy Lau concert tickets in Beijing knows, the best seats go for prices well above 1000 yuan. As advertised on these two websites, the most expensive stagefront seat is a bargain at 380 yuan.

In response to the article, the PiaoCN website is running a popup note graciously thanking the media for their concern, and reaffirming the presence of the two stars, the 28 May concert date, and the price schedule.

Links and sources:
The Beijing News article is here. Check out the screenshots documenting their investigation.
Two ticket sites: PiaoCN.com, and CTO, which still shows 29 April on the front page but has an altered date on the detail page.