Mumbai, May 23 -- A sharp rally in the unlisted shares of the National Stock Exchange (NSE) over the past two weeks has thrown a wrench into deals, with some sellers backing out from their commitments to deliver shares, leaving buyers empty-handed.

The unexpected surge in prices for the country's dominant stock exchange is fuelled by hopes of an imminent listing and attractive valuations, creating huge demand among investors and a significant supply crunch. Declaration of a rich dividend by NSE and its chief executive saying that its market share loss to rival BSE had "run its course" further boosted the demand for its shares.

NSE's shares in the unregulated unlisted market, where firms bound for prospective listing are traded between r...