A bug has been found in the latest version of WoWs. When you are detected, you will remain detected up to 20 seconds, regardless of what you do. Even if you hide in smoke or cruise outside of your concealment range, you will remain spotted for that time. In case you have situation awareness skilled on your captain, the warning will extinguish but you will still be spotted. If you happen to have incoming fire skilled on your captain, you might observe that you get the warning, apparently without being spotted previously.
The authorities (Wargaming) have been informed about this issue.
Issue confirmed by WG EU Community Contributor Flamu