Back Arrow - click twice?

Yesterday I noticed that when I viewed a thread and then pressed the back arrow it does nothing.  If I click the back arrow the second time it works and takes me back to discussion.

Thinking it might by my computer I shut it down last night.  But same problem occurs today.  Not every time, but say 90% of the time.

I can see the page icon blink on the first click and on the second click it does the "loading" message.

Has anyone else noticed this?