It all seemed to be going so well for The Hurt Locker's Oscar campaign.

A month- and-a-half ago, Avatarlooked like the clear favourite for the best-picture gong. Then, as we reported last week, wins at the Directors' Guild, Producers' Guild and at the Baftas nudged Kathryn Bigelow's war film level with her ex-husband's fantasy smash. Now, it has emerged that Nicolas Chartier, one of Locker's producers, has sent out an email urging Oscar voters to support his small picture and not – in an unambiguous reference to Avatar– "a $500m film". Negative campaigning may now be okay in politics, but it is regarded as very poor behaviour at the Oscars.

In such a close race, the bad feeling that has resulted could prove significant. Realising this, Chartier quickly performed a somewhat undignified volte face.

“My naivety, ignorance of the rules and plain stupidity as a first-time nominee is not an excuse for this behaviour and I strongly regret it,” he said. “Being nominated for an Academy Award is the ultimate honour, and I should have taken the time to read the rules.”

The recantation came a little too late and, in a near-unprecedented move, Chartier had been banned from attending the ceremony. For all that, the race still remains very close. Most bookies – defying all laws of probability – have both films odds-on to win. How does that work?