As per the contract
The issuer reserves the right purchase back the security at 1.1 times the highest price the asset was traded on GLBSE over the previous month.
To me this means that if the issuer is going to buy the security then it must be done at 1.1 times the highest price, otherwise the issuer cannot purchase the shares back. As the issuer is usagi then usagi must pay at least 1.1 times the highest price over the last month.
I would interpret the contract differently. That is, if the issuer wishes forcibly to buy back shares, it must be at 1.1 times the highest traded price. This right is reserved. It does not say that this is the only situation in which the issuer may buy back shares if sellers are selling voluntarily for a lower price.