Mutual funds attracted $47.5 billion in net inflows in March, mostly into bond funds, a trend that has endured for 27 straight months, according to Morningstar.

Taxable bond funds brought in $31.7 billion in March while municipal bond funds added another $3.9 billion. During that period, U.S. equity funds raised just $1.3 billion, although this was an improvement over February, which was a negative month for U.S. equity funds. International funds brought in $6.6 billion in March.

“It’s a continuation of the trend we’ve seen for more than two years now,” said Sonya Morris, an editorial director at Morningstar [MORN]. “It’s due to a couple of factors: low-yielding alternatives, such as CDs and money-market funds; and 2008’s volatility is still prominent in investors’ minds. They’ve rejiggered their portfolios to lower-volatility asset classes.”

Money market funds lost $148.2 billion in March, mostly to bond funds. Morris notes that investment in money market funds soared in 2008, when the government said it would guarantee them. Money market fund assets held steady at around $3.5 trillion until mid-2009, but since then they have fallen by $739.6 billion. Money-market fund assets are still way above where they were before the crash, though. At the end of March, these funds accounted for $2.9 trillion.

By comparison, money-market fund assets peaked at $2 trillion between 2000 and 2006.

Meanwhile, investors poured $19.7 billion into exchange-traded funds and 18 new ETFs were introduced last month, a busier-than-usual period for the investment vehicle. In what seems like a reversal of mutual-fund trends, U.S. stock ETFs pulled in the lion’s share of assets, $10.9 billion, distantly followed by taxable bond ETFs at $4.4 billion.

But March’s results, which saved the entire quarter from net outflows—it registered overall inflows of $7.7 billion, or 39% of March’s inflows—are difficult to draw a concrete conclusion about. This is because of the way institutional investors use State Street’s SPDR, the original and largest ETF on the market, with $77.8 billion in assets and accounting for 9.5% of the ETF market. (By comparison, the next most popular ETF, the SPDR Gold Trust, is half the size.)

Morris said that January’s huge outflows from U.S. equity ETFs were primarily from the SPDR, which institutional investors move in and out of to manage their cash flows. Traditionally, December sees a flood of orders come in as investors try to take advantage of the tax year, and she said there simply isn’t time to allocate all of those assets all at once, so institutional investors park them in the SPDR so that money is in the market. They probably then sold out of SPDRs as they moved into strategic stock allocations, hence the outflows in January.

March’s massive inflows are a mystery, though: Morris says that while her explanation of January’s outflows is an educated guess, she has no explanation as to why traditionally secretive institutional investors were jockeying in and out of SPDRs at the end of the quarter.