Microsoft may be forced to delay the release of the next version of its productivity suite, Office 11, after introducing changes to the source code.
Office 11 went into its second phase of beta testing in March. Microsoft would normally ship the product after completing this stage.
But the company has now confirmed that "customer feedback" persuaded it to incorporate some improvements.
These will be made available for further testing, and the "refresh code" is expected to be available to download in June.
Office 11 is scheduled to ship in the summer, but this second series of beta tests raises doubts over whether Microsoft can meet the deadline.
"There is no target date set for release yet. The key is to get the product right, rather than just get it out there," said a spokeswoman for Microsoft. "We still expect [Office 11] to be released this summer."
Customers that signed up to Redmond's controversial Licensing 6.0 programme are expecting a version of Office 11 to be available from November under the terms of their contracts, whether they intend to upgrade or not.
Microsoft was unable to provide details of the improvements being made to the beta software.
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