In version 2.6.7 you can send the same coin without waiting for the 10 block confirmation.

I can't reproduce this. The 10 block lock-time is a consensus rule, so the transaction would get rejected by the network. Is that what happened?

The incident report was published. Ping @tusker.

https://featherwallet.org/changelog/

I will post an incident report later today detailing what went wrong and the lessons that were learned.

Edit: https://featherwallet.org/changelog/

I fixed an issue that could cause this. Let me know if you still encounter this after the upcoming release.

Thanks for reporting! Fixed. Will try to follow up with another point release soon.