WITHIN days of the tenth anniversary of the first “six-party” talks, aimed at getting North Korea to give up its nuclear-weapons programmes, two columns of steam rose from the nuclear complex at Yongbyon, north of the capital, Pyongyang. Shut down in 2007 in a deal that supplied the North with fuel oil, Yongbyon’s gas-graphite reactor can produce a bomb’s worth of plutonium a year, according to a report by the Johns Hopkins School of Advanced International Studies (SAIS). The news has put a damper on a recent upswing in relations on the Korean peninsula that followed North Korean tantrums, including a nuclear test, earlier this year. The two Koreas have restored military hotlines. On September 16th they reopened a joint factory complex at Kaesong, just north of the border. And on September 25th the regime in Pyongyang is to allow around 200 relatives separated in the Korean war to meet in the North in the first family reunions for three years. Even food and medicines have begun to trickle through.

A damper perhaps, but hardly a surprise. The North announced a reboot of its 1960s clunker in April, and satellite imagery of the complex has since revealed steady progress: expansion of its uranium-enrichment facility and the finishing touches on a new light-water reactor. But much is still unclear. International inspectors have not set foot there since 2008.

Outside interpretations vary. The old reactor may not even be up and running, the steam all for show, Bruce Bennett at RAND Corporation, an American think-tank, suggests. North Korea may, after all, be keen to attract the attention of America, which has recently affected indifference towards it.

But Suh Kune-yull, a nuclear engineer at Seoul National University, says the steam might even have been a mistake. When the reactor was linked to a cooling tower, dismantled in 2008 as part of the aid deal, steam was a reliable indicator of operation. Now the cooling process is done with river water; in this set-up, steam could indicate a serious leakage from the turbines themselves. Much of the plant is ropy: the graphite is well past its shelf-life, and the North’s electricity supply, needed to run the cooling system, is unreliable.

Jeffrey Lewis, co-author of the SAIS report, expects the North soon to invite international experts to Yongbyon to “show off” its new capability. Kim Jong Un, the North’s leader, might use concern about his nuclear programmes as a bargaining chip—accepting monitoring at Yongbyon in return for foreign aid. He can, says Daniel Pinkston of another think-tank, the International Crisis Group, still keep much of his military nuclear programmes secret.

Meanwhile, cash for the regime will now come back on tap from Kaesong, the wages for whose 50,000 workers are paid to the state. Mount Kumgang was open as a tourist site for South Koreans until 2008, when a North Korean soldier shot a visitor dead; that complex may soon reopen, too. The dictator’s gamble, says Mr Pinkston, is to “delink” progress on Kaesong and Mount Kumgang from nuclear issues. Part of that involves acting reasonably on inter-Korean projects. On September 14th, at an international weightlifting competition in Pyongyang, the South’s national anthem was played and its flag raised for the very first time.

South Korea’s foreign ministry says that denuclearisation and inter-Korean progress are “mutually reinforcing”. Park Geun-hye, the president, may wait for much clearer signs of mischief—another underground test, perhaps—before reluctantly freezing this summer’s gains. Park Ji-young of the Asan Institute in Seoul says the mercurial Mr Kim is “always moving in two opposite directions” so as to keep the negotiating advantage. Or maybe he just has trouble keeping a consistent strategy in mind all the time. Either way, it does not make Ms Park’s life easier.