When there is only one key I use this function to check when one key is released:
if (GameApp::event.type == sf::Event::KeyReleased && GameApp::event.key.code == sf::Keyboard::Right)
{
}
But when there are two keys pressed at the same time and I release one the event it's not handled.
PD: Sorry it's solved, the code works but I was checking inside a function that it's executed only when a key it's pressed so I wrote again the function.