Source: Microsoft

2015 was a great year to be a Microsoft (NASDAQ:MSFT) shareholder. The Windows maker's stock rose roughly 20% as a series of strong earnings reports and impressive announcements pushed shares to levels not seen in more than a decade.

Still, not everything worked in Microsoft's favor. Let's take a look at some of the more unfortunate events that weighed on Microsoft shareholders in 2015.

Microsoft stumbles on disappointing quarterly results
Microsoft shares experienced their largest drops of the year following two of the four quarterly earnings reports the company turned in during 2015. First in January and again in July, Microsoft shares moved lower after the company posted results that were largely in line with analyst expectations.

In January, Microsoft earned an adjusted $0.71 per share on revenue of $26.5 billion -- roughly matching analyst expectations. Microsoft's commercial cloud revenue rose 114% on an annual basis, as demand for Microsoft's cloud services, including Office 365, Windows Azure, and Dynamics CRM surged. Microsoft reported that it had 9.2 million subscribers to Office 365. Still, investors may have been expecting more. Microsoft shares fell more than 4% following its January earnings release. The performance of its Windows business may have contributed, as Windows OEM revenue slipped 13% from the same period in the year prior.

Microsoft's results were similar in July. Microsoft shares fell about 4% after the company recorded its largest loss ever. The firm recorded a massive $7.5 billion charge on its failed acquisition of Nokia's handset business. On an adjusted basis, the company earned $0.62 per share on revenue of around $22.2 billion in its fiscal fourth quarter. That was actually better than what analysts had been anticipating, but not to a great extent. Demand for Microsoft's commercial cloud products continued to rise, with revenue surging 88% on an annual basis. Windows revenue continued to contract, falling 22%.

The future of Windows Phone looks bleak
Microsoft's mobile platform, Windows Phone, remains troubled, and is quickly reaching the point of total irrelevancy (if it wasn't there already). On Dec. 3, research firm IDC updated its smartphone market projections, and the report wasn't good news for Microsoft's smartphone platform.

Although demand for smartphones has begun to slow, IDC expects Android and iOS-powered devices to finish 2015 on a positive note, with shipments rising on an annual basis by 9.5% and 17.3%, respectively. Windows Phone, however, will contract, with annual shipments dropping 10.2% this year. Given that it's operating from a smaller base, that's particularly alarming. Microsoft unveiled two new Windows Phones in October, but neither is expected to have much of an effect on the platform, at least not in the near future. IDC no longer expects Microsoft's share of the smartphone market to grow much in the coming years, and believes it will end 2015 with smartphone market share of around 2.2%.

That's unfortunate, given that smartphones are increasingly the dominant computing platform, and, for a growing number of users in established economies, the only way to access the Internet. Microsoft believes that its new Windows Phone feature, Continuum, will help it attract users, but it's in an increasingly precarious position. Even with strong Windows 10 adoption, Microsoft's inability to make headway in the smartphone market makes the future of the Windows platform as a whole less than certain.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.