F&P Healthcare led the market lower, down 4.2 per cent to $11.85 in average trading. A2 Milk fell 3.4 per cent to $10.75 and Comvita declined 3.3 per cent to $5.28, both on light volumes.
Trade Me slipped 0.2 per cent to $6.32 on a volume of 14.4 million shares, compared to a 90-day average of 534,000. The online marketplace's board has entered into a scheme of arrangement with UK private equity firm Apax Partners, who will pay $6.45 a share if shareholders agree.
Williamson said it's close enough to the takeover price that some investors are willing to take the money now rather than wait until next year, whereas buyers will be seeking some arbitrage or hoping another bidder comes out of the woodwork.
Outside the benchmark index, Methven soared 32 per cent to $1.52 after receiving a takeover offer from ASX-listed GWA Group at $1.60. The deal is also through a scheme of arrangement, and the Australian firm will also let Methven pay an interim dividend for the six-month period ending December 31.
Williamson said the deal was good for investors, but not so much for the broader market.
"We're going to lose another company from the NZX and you're left wondering if it's a case of turning the lights off if you're the last one to leave - it's not good."
NZX was unchanged at $1.
Spark New Zealand fell 1.4 per cent to $4.25 on slightly heavier trading than usual at 3.3 million. Meridian Energy rose 1.5 per cent to $3.40 on a volume of 2.1 million.
Of other companies trading on a volume of one million or more shares, Kiwi Property Group declined 1.1 per cent to $1.345, Auckland International Airport was down 1.8 per cent at $6.97, Z Energy rose 1.2 per cent to $5.80, and Contact Energy gained 1.4 per cent to $5.88.
Fletcher Building fell 1.4 per cent to $4.84 as investors continue to wait for news on the sale of its Formica international business.
Infratil declined 1.4 per cent to $3.57 after saying a delay to the sale of its Longroad Energy asset won't affect earnings guidance. Separately, it also plans to invest A$50 million in its Canberra Data Centres unit.
Kathmandu Holdings rose 3.7 per cent to $2.80 in light trading, posting the biggest gain on the NZX50 on the day.
Scales Corp increased 1.2 per cent to $4.27 after buying a 60 per cent stake in US petfood firm Shelby JV for US$23.2 million, and saying it plans to fund the company's growth aspirations.