Heavy PulseAudio user here, and occasional developer on the project. Pulse is very unlikely to be doing what you describe itself, it is probably something further up the stack in your desktop environment or whatever that is helpfully trying to manage Pulse for you, or alternatively some plugin that your distro added. This sort of demonstrates one problem with Linux - the fragmentation.
OTOH, my Windows 10 computer displays almost exactly the behaviour you describe - when plugging headphones in, some applications will inexplicably continue using the speakers. Volume levels change without any obvious reason between different connections of the same device. Sometimes I have to select the speaker output and then the headphone output and it will magically start working. All of that would be fine, except for the real problem: there is basically no way for me to properly debug and solve this problem, whereas solving your problem on Linux would be relatively trivial for anyone with a bit of experience, even if it is in fact a bug in Pulse.
> there is basically no way for me to properly debug and solve this problem, whereas solving your problem on Linux would be relatively trivial for anyone with a bit of experience, even if it is in fact a bug in Pulse.
I've never been able to debug any of this. I think "a bit of experience" is putting it lightly. I have no idea how to fix any of this and none of the documentation helps. Imo, between "being configurable but being impossible to configure" and "not configurable except for the most important bits, but at least you get a GUI that makes sense and does what you want and expect", I prefer the latter. I don't want to become a PA developer before I'm able to make it do what I want.
Also, if you dive into the Windows 10 sound settings, you can set the default device and the volume for every application and it'll never deviate from that unless you explicitly change it again. This is how it should be, and I don't understand why PA isn't capable of this as far as I can see.
And if a program deviates from that setting for any reason, the only other reason why it could deviate is because the program itself has changed it, and you just need to check that program's settings. There's two places to check. On Linux? No idea. Infinite possibilities.
> Also, if you dive into the Windows 10 sound settings, you can set the default device and the volume for every application and it'll never deviate from that unless you explicitly change it again.
Yes, I've dug deep in the Windows 10 sound settings many times. I promise you, it regularly deviates from it, in ways that don't seem at all deterministic. Your solid belief in Windows 10's sound system not containing any bugs doesn't jibe with my experience of it :)
As mentioned in my previous comment, I suspect there's something other than PulseAudio causing your issues, like some external tool (possibly bundled as part of a desktop environment) trying to manage the sources/sinks/volume. Because of that hunch I'd probably suggest your distribution's bug tracker as the appropriate place to report the issue, as it's likely an issue of integration.
I'm just a regular user sand my experience is more like yours. PA used to be terrible but for the last 5 years, at least, I've had no problems with it.
I just started using MS Win last year and sound is such a pain to configure in comparison, for me.
OTOH, my Windows 10 computer displays almost exactly the behaviour you describe - when plugging headphones in, some applications will inexplicably continue using the speakers. Volume levels change without any obvious reason between different connections of the same device. Sometimes I have to select the speaker output and then the headphone output and it will magically start working. All of that would be fine, except for the real problem: there is basically no way for me to properly debug and solve this problem, whereas solving your problem on Linux would be relatively trivial for anyone with a bit of experience, even if it is in fact a bug in Pulse.