It was the end of 2013 when Microsoft (MSFT -0.32%) announced the good news: In cooperation with Facebook (META -0.43%), its Windows applications and Windows Phone OS officially supported the wildly popular social media king. As the partnership matured, Microsoft expanded its integration and began referring to it as "Facebook Connect." Good news all around, particularly for the struggling Lumia smartphone line-up running Windows Phone.

Facebook Connect didn't dramatically boost Lumia sales, though Microsoft did move 8.6 million units last quarter, and other apps integrated with Facebook including the wildly popular Office 365 are continuing to grow by leaps and bounds. No, the growth of Microsoft's services aren't due to integration with Facebook, but it sure hasn't hurt. Alas, a recent "tweak" to Facebook's application programming interface, or API, has put a halt to Microsoft's Connect feature, just as it's preparing to launch the much anticipated Windows 10 OS.

What's an API, and who cares?
The value of an API is that it enhances a software's ability to utilize new features as they become available, but most importantly in Microsoft's case, makes it possible to seamlessly integrate with other applications. The result is that with little more than some behind-the-scenes development work, an API gives companies like Microsoft the ability to expand the capabilities of its own apps, including Outlook, Photo Gallery, and Windows Phone, among others.

As Microsoft put it, Facebook's API, "brings contact information from your Facebook friends into and the Windows People app, keeps those contacts up-to-date, and provides options in apps and services like Photo Gallery, Movie Maker, and to share to Facebook."

Naturally, Facebook is aware that thanks to its API, users were able to access many of its features and functions -- say, posting a photo to "friends" from Microsoft's Photo Gallery -- indirectly. Which is likely the reason for the recent update to its Graph API. Going forward, Windows and Windows Phone users will need to access Facebook directly to accomplish a number of functions that were available via Microsoft's OS.

The impact
Prior to the API update, users were able to automatically sync Facebook friends with Outlook contacts so that an update on a friends account would seamlessly update as a contact. For example, a friend sends an invite via her Facebook account. Before the API change, the invite would instantly "ping" an Outlook user, whether she was logged into Facebook or not: no longer.

Windows Phone People app newsfeed will no longer be synced with Facebook's Newsfeed, and posting to the social media king's site using the Windows 8.1 People app has also been nixed. Bottom line, Facebook has cut the third-party chord and virtually all devices running a Microsoft OS are no longer synced.

Naturally, there's a workaround, which includes a seven-step process from Facebook's site. It's not a necessarily difficult workaround, however simplicity is king as it relates to devices, and user expectations are increasingly growing. Whether consumers are using a tablet, desktop, or smartphone, users are demanding a more complete, seamless user experience -- and Microsoft has been forced to take a step backward.

The fact that the API change affects Facebook is what makes this recent news a bit distressing for Microsoft. As it stands, it's estimated that an astounding 35% of the time consumers spend on mobile devices is devoted to Facebook or a Facebook-owned property. That is going to sting Microsoft, particularly its Lumia sales efforts, which aren't nearly as entrenched as Office 365.

That said, Facebook's API tweak shouldn't send investors running for the hills. Microsoft will almost certainly take steps to fix the lack of Facebook integration, either through high-level talks or future development efforts. But even if app users are "forced" to access Facebook the old-fashioned way -- directly -- it's not the end of the Microsoft OS world, however, it warrants monitoring going forward.