Nippon Ichi announced today that it has removed Criminal Girls from PlayStation Vita's backwards compatibility list. When played on the Vita, the PSP title has a bug where some of its sound will not play back. After an investigation, Nippon Ichi determined that the issue was with the Vita specifications, forcing them to remove the game from the official list of backwards compatible titles.
Source
http://andriasang.com/comzfj/criminal_girls_vita/
Very bad news as this could be a widespread problem once more PSP titles are added to the compatibility list. If a really major title like Disgaea or a Final Fantasy title ends up like how Criminal Girls ended up, it could be trouble for Sony. It also officially confirms that PSP emulation is software only which makes things worse.