The bid vehicle of former BP Plc
The stock traded down 6.5 percent at 929 pence at 1035 GMT, lagging a 2.3 percent drop in the STOXX Europe 600 Oil and Gas index <.SXEP>, on lower crude prices.
Worries about the partners Hayward had taken on, and a rise in risk aversion among investors, amid market turbulence, outweighed positive news flow around Kurdistan since early September when the deal was announced and the shares suspended.
Given the positive news around the Exxon deal, you would have expected the shares to move up, said Tim Hurst-Brown, oil analyst at Mirabaud Securities.
There may be a corporate governance concern among some people and the risk environment is different now than when the deal was agreed, he added.
Hayward was seen to have bought oil reserves for a modest price, analysts liked his plan for further acquisitions in the region and a deal between the regional government and Exxon Mobil lifted other Kurdish explorers' shares, as it was seen to be prelude to an end to an impasse on oil revenue sharing.
The shares were also expected to get a lift from the fact the company expects to enter the FTSE 100 index of the UK's largest companies, which means passive, tracker funds will be forced to buy its shares.
The deal marks Hayward's return to a senior management role in the oil business after being forced out of BP following the Gulf of Mexico oil spill. He will be CEO of Genel Energy Plc.
However the deal has been criticised for giving Genel's former owners a fast-track route to a London Stock Exchange listing -- something they previously tried to achieve before one of them, Mehmet Sepil, received a 1 million pounds fine from regulator the Financial Services Authority for insider dealing.
Mehmet Karamehmet, the other major shareholder, was accused in a U.S. diplomatic cable posted on the Wikileaks website of issuing death threats to a former business partner.
Earlier this month Turkey's appeals court called for his retrial on charges of embezzlement, after a previous conviction was overturned.
Karamehmet and Sepil will own around half of Genel Energy.
The FTSE Group said earlier this month it was looking at tightening entry requirements for its UK indices in response to investor concerns it is too easy for companies with low free floats and hazy corporate governance standards to join the prestigious FTSE 100.
The Association of British Insurers, whose members own 20 percent of the UK stock market, is worried stocks enter the FTSE 100 too easily and is exploring ways to put would-be entrants under closer scrutiny, an insurance industry source told Reuters.
Hayward and Sepil have said in interviews recently they thought the Kurdish assets of Norway's DNO
However, Baghdad refuses to recognise the contracts the Kurdish authorities have signed with foreign companies and has withheld payment for oil, which must be shipped out through territory controlled by Baghdad.
(Editing by David Holmes and Mike Nesbit)