I realize this is an old topic, but I recently upgraded my word press account and I am experiencing the same hyperlink issue, which did not happen prior to upgrading.
I have tried emptying my cache and switching from Safari to Firefox but so far, nothing seems to be working.
I am highlighting the text I wish to link, clicking on the link button where the insert/edit link box pops up to enter the URL. I enter it, click “add link”, and then it brings me back to the Post page, and does not add the required URL.
Please help!