Copying and pasting using shortcuts is not working in MacOS

Replication steps:

1. Load http://qt.io
2. Select some text on the page with  mouse.
3. Copy using Cmd + C
4. Paste it into a text editor of your choice

Or 

1. Visit http://google.com
2. Write some words into the search field
3. Select the text and use the copy shortcut on your keyboard, then use the paste shortcut to paste it into the browser URL bar.
4. Repeat the same by copying from the URL bar into the search field in the web page.