They may also have picked up a currency gain taking their money home as the kiwi dollar advanced on its Australian counterpart, he said.
MRP shares have since recovered, trading recently at $2.42. The shares are rated a 'hold' based on the consensus of six recommendations compiled by Reuters, with a median price target of $2.50.
Forsyth Barr analyst Andrew Harvey-Green put a 12-month price target of $2.35 and a rating of 'hold' in a report dated June 19. His discounted cash flow valuation was $2.18, including a discount of 20 cents for the Labour/Greens policy for a single buying agency. It also assumed wholesale electricity price growth of 2 per cent a year and electricity demand growth of 0.7 per cent.
"Whilst we like the underlying industry characteristics (robust earnings & solid growth), there are regulatory (single buyer model and transmission pricing) and demand issues (threat of aluminium smelter closure and generally weak demand) facing the industry," he said in the report.
Harvey-Green called MRP "an attractive business in an industry that has a solid earnings track record." He forecasts a gross dividend yield of 7.2 percent for 2013, rising to 7.8 percent in 2014.
Nominee companies are typically custodians that hold and administer securities for the actual owner. The ultimate owners often can't be easily identified.
The second-largest shareholder in MRP as at June 21 was New Zealand Central Securities Depositary, the Reserve Bank-owned company that holds shares for its NZClear members, which include banks, fund managers, custodians and trustee companies. Its holding reduced by 2.2 million shares to 194 million, second only to the Crown with 724.6 million shares, or 51.76 per cent, of MRP.