Itseez/opencv — pull request #1109 by nikman-ru (2013-07-11 11:25:33+00:00)
Title: Fixed VideoCapture::open() does not release previous capture sources (Bu...

...g #3150).

VideoCapture didn't call release method and just ignored the new capture sources.
OpenCV documentation:
bool VideoCapture::open(const string& filename);
bool VideoCapture::open(int device);

The methods first call VideoCapture::release() to close the already opened file or camera.