Alibaba Group updated its registration statement yesterday to include first quarter financial results, and while a slowdown in revenue growth startled Yahoo! Inc. (NASDAQ:YHOO) investors, there’s still plenty of reason for the rest of the market to be excited about the upcoming IPO.

Alibaba

Revenue drops as mobile makes up a larger mix of total volume

The biggest potential worry is that revenue growth fell to 38.7% year-on-year in the first quarter, well below the 61.7% year-on-year growth the previous quarter. Seasonal effects likely play a role, but even if the growth rate stays in the 30s from here on out, that’s still an incredible rate. Gross merchandise volume (GMV) fell to 46.3% annual growth from 52.9% the previous quarter, reflecting a higher mix of mobile which monetization rates two-thirds lower than desktop.

“We believe the bulk of the disconnect between revenue and GMV is due to mobile – mobile GMV increased to 27.4% of GMV vs. 19.7% the prior quarter and 10.7% the prior year,” UBS analyst Eric J. Sheridan wrote in a note yesterday.

Alibaba Group also released GMV data for Taobao Marketplace and Tmall for the first time yesterday. Taobao GMV grew 32.3% year on year, down from 35.7% in 4Q13, while Tmall grew 90.1% compared to 101.1% the previous quarter.

Yahoo’s stock price gets support from its stake in Alibaba

Yahoo! Inc. (NASDAQ:YHOO)’s stake in the company has also apparently dipped, from 22.6% in the last filing to 22.5% in yesterday’s update, compared to 24% in Yahoo’s first quarter filing. Yahoo is still slated to sell 208 million shares at the Alibaba Group IPO (though we still don’t know exactly when that’s happening) and Sheridan doesn’t see any reason to adjust Yahoo’s sum-of-the-parts valuation based on this tick down, maintaining a Buy-rating with a $47 price target. Investors were more concerned about the revenue slowdown, and Yahoo’s stock price fell from just under $37 to $34.81 because of Alibaba’s filing.

There has been a lot of concern about what will happen to Yahoo! Inc. (NASDAQ:YHOO)’s stock price once Alibaba goes public because investors will be able to invest in it directly. This doesn’t change Yahoo’s fundamental value, but if the price is being supported by investors’ desire to own Alibaba, which yesterday’s drop seems to confirm, that support could dry up in the near future.

The filing also revealed that Yahoo! Inc. (NASDAQ:YHOO), along with Softbank Corp (TYO:9984) (OTCMKTS:SFTBF), is expected to sign a voting agreement that would require it to vote in favor of Alibaba Partnership director nominees at future shareholder meetings.