Data tracked by the investment analytics firm of more than 800 primarily non-financial US-based companies show the buying was part of a broader move, as these firms have extended the duration of cash holdings and safe securities over the past 18 months. On April 9, the day that Trump said it was "a great time to buy" stocks, treasurers boosted their holdings further by purchasing about $5 billion of Treasuries that mature in one to three years, the Clearwater data show.

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"Over the last year or so we've been seeing a duration bent to longer maturities," said Matthew Vegari, head of research at Clearwater. "These type of corporate investors are taking advantage when yields are rising and buying. Overall, they have been shedding money market funds." 

The firm's clients pulled about $31 billion out of money market funds in April, the data show.

Most of the maturity extension comes as corporate treasurers seek to lock in higher yields ahead of and during the Federal Reserve's cutting cycle. On a total return basis, the Treasury market hasn't fared well this month, with yields moving higher in the wake of the US trade truce with China that was announced on Monday. Even though stocks have surged, two-year Treasury yields remain slightly higher, hovering at just over 4% as the outlook for Fed cuts erodes.

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"For these firms, owning these securities doesn't really give them too much duration risk because even if the bonds get pummeled, they're just going to hold to maturity anyway," Vegari said.

Swaps traders are pricing in two quarter-point rate cuts by the Fed this year, with several major Wall Street banks this week pushing back to December when they expect to see the first move. 

"The appeal of cash has certainly gone back up because the market is pricing in fewer cuts," Vegari said. The question now is whether corporates continue to purchase slightly further out on the curve, he said. "I don't think they know the answer to that yet — it's likely to be really a 'wait and see' for them."