Can't open a stacked set of photos

Greetings,

I am using Elements 14.  In Organizer I selected a series of photos and right clicked on the last selected photo.  The drop box appeared with the Stack option.  I selected Stack and Stack Selected Photos and left clicked on it.

The photos stacked instantly and the stacked icon appeared in the upper right hand corner.  However the right facing arrow on the right side of the photo did not appear and now I cannot unstack them.  When I right click on the stacked photo or go through Edit / Stack, the stack options are grayed out.  How did I screw that up and how can I get them unstacked.

As always, thanks for your help!

Mark