Bonds performed so poorly in the past month that exchange-traded fund investors were forced to buy in record amounts.

An unprecedented $4.8 billion flooded into the $20 billion iShares 20+ Year Treasury Bond ETF (ticker TLT) as the ETF sank 5.6%, according to data compiled by Bloomberg. It was a similar story for the $83 billion Vanguard Total Bond Market ETF (BND), which absorbed $3.1 billion last month amid a 2.9% dive.

While the case could be made that bargain-hunters were attempting to time the bottom, it’s more likely that money managers with allocation limits between stocks and bonds had to rebuild their fixed-income exposure heading into quarter-end. While those investors likely had to buy equities as well, the selloff in debt was even more fierce -- potentially driving the record flows into debt ETFs.

“Theoretically, if you have a 60/40 portfolio or some diversified mix of equities and bonds, when you rebalance, you sell winners and buy losers,” said James Seyffart, Bloomberg Intelligence ETF analyst. “In this case, equities and bonds are both down year-to-date but bonds are down more -- so that would potentially mean buying fixed-income ETFs at the end of the first quarter and selling equity ETFs.”

TLT and BND have plunged 10% and 6.5% this year, respectively, which would rank among the worst annual performances ever for both funds. By comparison, the $420 billion SPDR S&P 500 ETF Trust (SPY) has fallen 4.9% so far in 2022.

Overall, government debt ETFs posted inflows of $11.2 billion in March, a month where Treasury yields screamed higher as inflation rose to multi-decade highs and the Federal Reserve lifted interest rates.

“These funds systematically rebalance, “ said Ben Carlson, director of institutional asset management at Ritholtz Wealth Management. “Since bonds sold off these funds would have to buy to stay in line with their target allocations.”

Other theories exist beyond portfolio rebalancing. Vanguard ETFs, for example, are likely to see inflows “rain or shine” from asset allocators, Seyffart said. There’s also the potential that even as bonds sold off, investors seeking havens amid Russia’s invasion of Ukraine poured money into the safety of Treasuries.

“I don’t think you can discount the fact that some folks still see bonds as a safe haven, even given the rising rates story,” said Dave Nadig, financial futurist at research firm ETF Trends. “With massive global macro headlines, tough to pin down.”

This article was provided by Bloomberg News.