Contradicting statements from Mylan Inc. (MYL) and the U.S. Food and Drug Administration have created confusion about an investigation into quality control issues at the generic drug maker's West Virginia manufacturing facility.

The confusion sent Mylan shares on a roller-coaster ride Tuesday. It began after a Pittsburgh Post-Gazette story Sunday said that employees at the plant had covered up computer-generated warnings about the drugs produced there.

Mylan said Monday that the issue had "no impact on the quality of our product." Tuesday, the Pittsburgh company issued another press release saying the FDA had visited the Morgantown manufacturing facility on Monday and determined that "the baseless accusations in the article were unfounded."

The FDA later disputed Mylan's comments by saying its investigation is ongoing.

"The agency has formed no conclusions at this time. Statements to the contrary are untrue," Steven Solomon, FDA's assistant commissioner for compliance policy in the Office of Regulatory Affairs, said in a statement.

In response to the FDA statement, a Mylan spokesman said "our CEO would never have gone out with a statement like that without being informed of the closeout of the FDA inspection." Officials from the FDA weren't immediately available to respond to Mylan's latest comments.

Several analysts hypothesized there may be a communication breakdown between the local inspector, who may have made comments to company officials, and the official FDA assessment of the investigation as a whole.

Mylan shares recently rose 4.8% to $12.68. The stock has been volatile Tuesday, rising as much as 10.5% before sliding 1% lower than Monday's close after the FDA's statement. The company is scheduled to report second-quarter financial results Thursday morning.

The Post-Gazette reported Sunday that Mylan had launched an internal probe to investigate whether workers at the plant had been routinely overriding computer-generated warnings about the drugs being produced at the plant. The newspaper cited an internal report and had other experts review the report and call it a significant problem.

Tuesday, Mylan said the agency "noted there was no evidence of any data deletion. All data was reviewed and was present and accounted for."

In an emailed statement, Executive Editor David Shribman is quoted as saying the Post-Gazette stands by its reporting in the Sunday article.

In response to the article, several analysts highlighted Mylan'sstrong manufacturing reputation. But that perception is balanced with the FDA's ongoing vigilance in making sure that copycat drug makers are meeting required standards.

Caraco Pharmaceutical Laboratories Ltd. (CPD), Novartis AG's (NVS) Sandoz unit, and K-V Pharmaceutical Co. (KVA) have all been subject to facility-related issues in the past year that have led to major product recalls for the companies.

Even Indian generic companies, like Ranbaxy Laboratories Ltd. (500359.BY), are under pressure from the agency over quality controls and manufacturing practices at their plants.

-By Thomas Gryta, Dow Jones Newswires; 212-416-2169; thomas.gryta@dowjones.com