its a signing bug.

There have been incidents of 'accidental inflation' of fully-anonymous cryptocurrencies (as opposed to 'semi-anonymous' [sender/receiver anonymous] and pseudonymous bitcoin).

Zerocoin had a 1/4 inflation from https://news.ycombinator.com/item?id=13672117

I wouldn't go so far as to say this is will prevent this technology from ever being secure. Its early days. Don't play with what you can't lose.

The great monero team did notify other CryptoNote based currencies, it seems that the granddaddy Bytecoin didn't fix it before the notification period. There is no evidence that they exploited this. They even came up with a method for detecting if it had been exploited...