Shares of data storage giant EMC (NYSE:EMC) reported strong fourth-quarter earnings this morning, sending investors into a frenzy. The stock opened 6% higher this morning -- but started losing steam immediately, until EMC's share price had fallen below Wednesday's closing price.

Why did the market greet EMC's report with such a manic-depressive response? Let's find out.

First, EMC did well in the fourth quarter. Analysts were looking for earnings of $0.68 per share on $7.1 billion in total sales.

With 5% year-over-year revenue growth, EMC fell short of the Street's sales estimates to land at $7 billion. Adjusted earnings per share, on the other hand, rose 15% to $0.69 per share. That's a modest positive surprise.

Looking ahead, EMC expects to see adjusted full-year earnings close to $1.98 in 2015, culled from revenues of about $26.1 billion. Here, analysts were looking for somewhat stronger figures, like $2.16 in earnings per share on sales of $26.2 billion.

Management explained this timid outlook with currency headwinds, as the American dollar keeps strengthening in comparison to other major world currencies. As a reminder, the value of the dollar has increased by 21% against the Euro in the last 12 months and EMC collects over half of its revenues abroad.

Image source: EMC

The core data storage division grew fourth-quarter sales by 2%, compared to the year-ago period. Cloud computing app development service Pivotal raised its sales by 18% and, as reported on Tuesday, virtual computing veteran VMware (NYSE:VMW) delivered 16% higher sales. In general, EMC's customers seem to be looking for commodity storage systems paired with high-quality management and analysis software. It's the value-added systems and exclusive software solutions that are driving EMC's growth nowadays, with the financial backing of a large and stable hardware presence.

All of these results were available in the early morning, well before EMC's price drop started. But the company still had more news to share.

At the market open, EMC had just concluded its conference call with analysts. In it, the company shared new details on how it wanted to treat its 80% ownership stake in VMware -- a sore spot that has been under criticism by activist investor firm Elliott Management.

As the call proceeded, analysts kept prodding EMC's management for more information on their VMware plans, but these pointed questions were expertly dodged. At the end of the call, just when the market bells were ringing, investors and analysts still had no new information on EMC's future VMware plans.

Elliott wants EMC to fully spin the acquired company back out again, or to find an interested buyer. The idea is to monetize the entire VMware asset while it's a hot commodity -- and EMC's leadership prefers to keep their 80% stake, profiting from VMware's growth more directly.

EMC CEO Joe Tucci is set to retire this year, and that change in control could open new lines of dialogue with Elliott. Or the as-yet unnamed replacement might clamp down and refocus on blending VMware even tighter into EMC's larger structure.

Investors hate uncertainty, and they are getting a lot of that with EMC right now. Trigger fingers are getting itchy, which makes price jumps more dramatic in every direction. A solid fourth quarter with economic headwinds for the coming year wasn't enough to soothe those rattling nerves, which is why EMC's stock bounced both high and low today.