I set Flash security settings on this adobe page :
These settings are reset to default when I "clear browsing data".
This is a security flaw that I first reported back when Opera 32 stable was released. It still hasn't been fixed in Opera 34 stable.
It only happens if you have checked "Delete cookies and other site data" under "Clear browsing data".
It's ridiculous that if you want to delete cookies, you also reset Flash security settings. And how many people even know that they reset their Flash security settings when they deleted cookies?
It's an Opera problem. The Flash settings are stored in a file named settings.sol which is buried deep in the Pepper Flash folder. There's no reason for Opera to do anything to this file.