From the press release by Akita prefectural government on July 25:
A resident in Akita Prefecture alerted the authorities when the bag of leaf compost that he purchased from a local garden/home center measured high in radiation with his portable survey meter. The authorities tested the content of the bag, and it had 11,000 becquerels/kg of cesium.
At the garden/home center (2 locations) the air radiation 1 meter from the pile of the leaf compost bags measured as high as 0.48 microsievert/hr.
The press release is somewhat misleading, as it says the air radiation 1 meter from one bag of the leaf compost is 0.06 microsievert/hr. If you measure in front of the pile of the same bags, the radiation is as high as 0.48 microsievert/hr. Akita's air radiation level (which the prefectural government measures only at 2 locations) is between 0.04 and 0.06 microsievert/hr.
According to Yomiuri Shinbun (7/27/2011), these bags were packed in Tochigi Prefecture, and 20,000 bags have already been sold in Akita Prefecture alone.
Shimotsuke Shinbun (local Tochigi paper; 7/27/2011) reports that Tochigi Prefecture tested the leaves that went into the leaf compost bags, and they found 72,000 becquerels/kg of radioactive cesium. The leaves were collected in the northern Tochigi in April, and was sold outside the prefecture from mid June to early July. The Tochigi prefectural government ordered the two sellers of leaf compost in Tochigi to recall what's been sold and refrain from shipping "voluntarily" (i.e. at the sellers' own cost, with no support from the government).
Leaf composts are mainly used by the home gardeners. There may be many who hoped to grow their own, radiation-free vegetables and bought these bags to amend the soil for better growth of the seedlings. Well, that hope is dashed. The home gardeners may have ended up contaminating their own soil which may not have been contaminated before they put in the compost.
The Ministry of Agriculture, Forestry and Fisheries couldn't even figure out that cattle farmers feed their cows with rice hay. What the individual home gardeners use for their small gardens was probably none of their concern, as the Ministry is there for the producers.