It's a single-click to expand a stack, and another single-click to collapse a stack. If you're double-clicking, you're effectively expanding/collapsing the stack, so you end up where you started.
How is that the answer to "How to Revert to Previous Version"? It's the wrong answer to yet some other question.
Sure - I have no idea what I'm doing. Have you tried a single-click? Doesn't work either. What double-click does is Expand & Select All in the stack, which has been working fine since forever - and neither work now.
I have copied all the previous files from the "C:\Program Files\Adobe\Adobe Lightroom" from another installation into my computer and while that seems like a horrible idea, it does appear to have solved the problem and is nowhere near as horrible an idea as updating to 6 in the first place was. I think the current job I'm working on will be my last in 6.x for a while until the bugs are worked out - back to 5.x which was fine.
BTW, Double-click and Single-click are completely different operations. Two singles <> one double. Everyone knows that.
Try dropping the attitude, eh?
Single click works to expand and collapse stacks on my Windows 7 computer running Lightroom CC 2015. If you haven't already, try disabling GPU acceleration and see if that makes a difference.
From Lightroom 3 on, double click would expand the stack and select all the photos in the stack. I haven't checked if this works in Lr6 although with all the other things Adobe has broke in Lr6 (and not fixed in 6.1) I wouldn't doubt this is broken too.
Thanks guys - I may try more trouble-shooting later when I get a chance, but my "hack" fix is working for the moment. Single and Double click on Stacks was working fine on CC 2015 until today when I did the update and the old executables (dated April 6 2015) from my wife's installation - thank goodness she had not yet done the update - have restored that operation. Sorry about the "attitude" but Lightroom is our main workflow app - my fault for being so cavalier about installing updates in a production environment. Years of fairly flawless LR updates lulled me into a false sense of "it will be OK". Bad idea!
I have already read a few other posts about even worse bugs, so I hope the "hack" fix continues to work - no idea how it will affect the CC app or Photoshop or anything else where code may be shared - yikes - seems like a can of worms. Oh, and then there's Photoshop too that I updated - no idea what surprises will be waiting for me there.
I have had mixed and seemingly random luck with GPU on/off - sometimes seems great, other times causes the entire work window to go black (even when not editing) and other odd behavior. For the last few days I have had GPU Off and even with it on, the benefit seems low.