The New Zealand dollar has held steady after gaining more than US1 cent in New York on Friday.
Westpac currency strategist Imre Speizer said stronger-than-expected employment figures in the United States should have meant a rise in the US dollar but, instead, the opposite happened.
Mr Speizer said there were a number of theories as to why that happened, such as that the market had been positioned for strong data, but none of them rung true.
Also puzzling was US Dollar Index, which was a "basket" of the US dollar against major currencies such as the euro, yen and Swiss franc.
"That US Dollar Index has basically struggled in the last few weeks, despite a string of fairly decent data. That's, I guess, the bigger puzzle," Mr Speizer said.
"It's not that Kiwi-US has done well, because Aussie-US has done also, and so have some other currencies against the US. It's really a question of 'why is the US dollar not going up, when the economic data is getting better'."
Just after 5pm, the New Zealand dollar was buying: 82.91 US cents, 91 Australian cents, 50.73 pence, 0.605 euro and 85.32 yen.
Top 50 Index up
The share market was little changed but the NZX Top 50 Index managed its first rise in seven trading days, gaining 5 points to 4718.
Forsyth Barr investment adviser Euan McIntosh said the market had been weak for several weeks after a strong year and that investors were possibly booking profits before Christmas.
Among individual stocks, Telecom rose 4.5 cents to $2.33 today after it announced it had sold its troubled Australian business, AAPT, for $A450 million - a move Mr McIntosh said was positive for Telecom.
Also today, there had been a rebound in some power company shares.
"We've seen Mighty River Power, Contact and Meridian's installment receipts are all up today and possibly that's after being viewed as oversold last week. This week investors are, perhaps, sensing that there's longer-term value at these prices," Mr McIntosh said.
Mighty River Power shares rose 3 cents to $2.03, while while Contact Energy gained 15 cents to $5.05. Meridian Energy's installment receipts were steady at 92 cents.