If you leave a tab open in youtube or facebook or similar 'super java timeout keylogger type advertising marketeer' websites, which mess with your keyboard shortcuts and browser functionality, then you will notice that links to youtube videos and similar, become dead and stop working (except the open in new tav method you mention).
This is in my opinion due to AJAX and Javascript timeouts programmed in to these websites
second reason being that Safari uses a lot of 'power saver' options which are not accessible to the user, but which are hard programmed in by developers. This is to make safari (seem to be) the fastest and best browser
However, its just a deception, because it is just deactivating what it considers unecessary for your browsing experience, in order to minimise the loading time.
a lot of websites have deliberately made safari unsupported (including google youtube until Tim Cooke decided to take 10 Billion dollars to switch back from Bing to Google search).
My advice, is not to use Safari for modern AJAX/java driven web apps (websites as we used to call them), and to switch to a non deprecated browser such as firefox.
I also cant upload images to google plus in Safari because the java upload dialogue does not work. Same to make a new folder for images in facebook. Doesnt work in Safari. Lots of things dont work in Safari, which is why i consider it to be a deprecated browser