Even with the markets rocketing, there's reason to be cautious about some aspects of the action, Jim Cramer said on

CNBC's

"Stop Trading!" segment Wednesday. "Today is a peculiar day because it is the best day for mutual funds to mark up stocks."

He also was uncertain about upcoming moves from

Federal Reserve

chairman Ben Bernanke, who speaks Thursday. "How could anyone be tough on inflation right now?" Cramer wondered.

Cramer also believed the market had undergone a significant change that might require investors to ride the wave up rather than sell into strength. "I am reluctant to sell given that this market feels very different from

last week's rollercoaster," he said.

But he cautioned against buying, saying "I'd wait until

Bernanke speaks" and he instructed viewers to wait and see if the market "does sell off at the end of the hour," a sign of weakness that has persisted in recent trading.

Still, it's very much a changed tone in the market, and you can credit

Citigroup

(C) - Get Report

.

"People thought that Citigroup wasn't anything. ... What's changed here is that it's very much a glass-half-full situation," Cramer said. He believes that Citi, which he owns for

Action Alerts PLUS, is sparking the rally.

At the time of publication, Cramer was long Citigroup.

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