When I duplicate layer the old layers no longer stay selected. Only the top layer stays selected leaving a bunch of interleaved, unselected layers.

It’s been a while since the change - previously, there was no interleaving but interleaving is actually preferred under the majority of use-cases. Perhaps a checkbox setting in the Prefs Dialog may be useful? And while they’re at it - add an intelligent aka FI aka Fake Intelligence aka AI Search Bar in the Prefs Dialog. 

And scripting + Expressions API/Methods for mask transforms will be good too.  

And Bonus Points if the results of the extents argument set to True for sourceRectAtTime(), specific for calculating stroke width was more human-friendly. :-D
BTW, I do have the formula but it’s not something usable 98.125367% of the time. So, perhaps an additional argument for stroke widths may be a good thing and won’t break existing architecture. 

sourceRectAtTime(time,true,simple) where simple means capturing the stroke width without the “hmmmmm” formula.