Happens to me too (LR CC 2015.5 / OS X 10.11.2). Please file a bug report in the official Adobe feedback forum: Photoshop Lightroom | Photoshop Family Customer Community. Be sure to include the exact version of LR (Help > System Info) -- "latest update" is ambiguous -- and version of OS X or Windows.
A workaround is to shift-click on the stack badge in the upper-left corner of the thumbnail -- that will expand the stack and select all of its photos. Then do Ctrl+Shift+H.
I've found a bug report filed here:
Hopefully this will be fixed soon, but for now I will be installing an older version to remedy the problem by following the instructions posted in the comments of that thread.
Great, be sure to vote (Me Too) the topic -- that will make it a little more likely that Adobe will prioritize a fix.