What is red ring around the outer edge of the display?

I went for a run/walk and put my watch into walking mode (which I've done many times before).  When I reached the end I noticed the display has a red ring all the way around the outside and the start/stop controls look different than normal.  I can't seem to "end my walk".  

It looks like I somehow put it in a strange mode but have no idea how or how to get out of it so I can save my walk.  Any help would be appreciated.

The forum is not allowing me to upload the image so I'll try to describe it.  I can see the usual metrics when walking, I can scroll around the watch by touching the screen and the top and bottom buttons both work, but the display shows a red circle around the outside edge of the display when I am looking at the walking metrics.  If I scroll left or right to the normal clock display (for example) the red ring is gone, so it's not a hardware problem.  On the metrics screen the red circle is interrupted by the icons for the button controls, but the only 2 icons seem to be a green "go arrow" which restarts the walk and a red "square icon" next to the bottom button which doesn't seem to do anything when I press the button.  The "red circle" disappears if I restart my walk by pressing the top right button next to the "green start" icon. 

So basically all functionality works but I can't "end my walk".

Any ideas?