I’m currently using Audacity 2.2.2 on Windows 7 & 10. When there are multiple Audacity windows open and you start playing in one window, you must now stop playing in that window before you can play in another window. In previous Audacity versions you could simply start playing in any open Audacity window and it would stop playing in the Audacity window that was playing. This is very valuable in several ways - one way is when trying to compare/set the same volume level in multiple windows. Another way is simply finding the window that’s currently playing can be challenging when there are many open windows.
This is basically the residual bug of this longstanding bug:
Personally I think the current behavior is perhaps “correct” - I would expect to have to stop play in one project (and not even just pause it, as in Bug 234) before being able to access play in a different project - you obviously disagree.
BTW you say that it behaved differently in earlier Audacities - I just tested on 2.2.0 and 2.1.3 and I get the same behavior you describe that we have in 2.2.2
The underlying issue that you have to understand is that Audacity was never designed from the ground up to handle muktiple projects open at the same time. It just happened to be enabled at some time in the long distant past by one of the developers - and done without any thought of the consequences of interactions (like the one you write about) between multiple open projects.
Your issue is just one of many that we know about and there are probably more - some of them we have patched - but basically
a) we are fundamentally undecided what to do
b) as a volunteer part-time project we are desperately short of developers
See this proposal to see the current stat of our thinking:
I will add your use case to the bug thread for Bug 234.
Update: Done - see https://bugzilla.audacityteam.org/show_bug.cgi?id=234#c12
It’s also made me look more closely at this related bug
Using the sliders in Mixer Toolbar in a Project-2 alters levels in on-going recording (or playback) in Project-1
And I just upgraded that from P3 to P2 as a result, to give it more focus