I like to add synths from synth rack using the "Synth Track Folder" option checked where it puts the synth and midi track into a folder when inserted into the project. I have to open the folders to see the midi track in PRV in 2017.4 I did not have to do that in previous versions with the track picker.
 
So now I have to go back and forth between track view and PRV opening and closing track folders in order to edit midi in the PRV.
Is this a bug?

Yeah i noticed the same thing. Its infuriating.

Tracks hidden using the Track View Track Manager also will not appear in the PRV.
 
There are 2 additional users in addition to myself posting reports of the same behavior since the release of SONAR [2017.04]:
http://forum.cakewalk.com/FindPost/3598682
 
http://forum.cakewalk.com/FindPost/3601466
 
http://forum.cakewalk.com/FindPost/3601627
 
I contacted customer support and sent them the contents of my post.  This is the response I got, which doesn't seem to answer my question about whether this new behavior is by design or not:
 
"Thank you for getting in touch with Cakewalk support. I’ll be happy to assist you.
Both PRV Track pane and Track view can be a selector of the PRV view focus. this gives you flexibility if you are using 2 monitors and place PRV in one of them."

stlstudio
So now I have to go back and forth between track view and PRV opening and closing track folders in order to edit midi in the PRV.
Is this a bug?

Seems like a bug to me, especially because if "Filter to Selection on Open" is checked and the track is selected, it doesn't open in the PRV.

http://www.cakewalk.com/Support/Contact/Problem-Report
 

I hear it's been fixed for the 2017.05 release.
 

SquireBum
Tracks hidden using the Track View Track Manager also will not appear in the PRV.

I doubt that's a bug...if you want a track hidden, you probably want it hidden wherever it might appear.

Anderton
I doubt that's a bug...if you want a track hidden, you probably want it hidden wherever it might appear.

Not even in my wildest nightmare!
Track view and PRV are totally different view setups in all of my projects once they get up and running.
I have no reason to see midi tracks in TV when the project is well under way and only want to see audio tracks in TV.
Then I want to see the midi tracks, that are feeding those audio tracks in PRV and only those.

I never record midi in TV unless it's the simplest little doodle in a 2 track project, and even then I'll switch to PRV to record if it gets interesting and serious.

If this is intended behavior then all I can say is OMG! ... and sticking with 2017.01 until things change.

And then an other scenario is needing to move clips around in TV and only having one midi track showing but having 20 or more in PRV and wanting to switch back and forth quickly just typing D.

I can think of plenty or reasons why this is a terrible idea.

I see what you're saying...different workflows. I want to have everything in the TV as my epicenter for the project; I duck over to the PRV when I want to edit something. I prefer to record MIDI in the TV because I want to know where I am in the arrangement (e.g., punching and such).
 
When the "closing folder makes things go away" gets fixed, you could hopefully just dump all the your TV MIDI Tracks into a folder to take up virtually no space, and still be able to work with them individually in the PRV.
 
I already do something similar when I get into a project's closing stages. After converting instruments to audio, I move all the MIDI tracks to the end of the track list. That way only the mixable audio tracks show up in control surfaces, but the MIDI tracks are still there if I need to touch anything up.

I've come to isolate sections by screenset (all locked except for [1] after a day or so into the project)

[1] Everything in TV + All midi in PRV and all tracks and busses in Console.
This is where I'll copy and move clips or do any midi clip editing.

[2] Strings (16 or more tracks) ***but only Audio in TV, midi in PRV and only those tracks and buss in console
[3] Brass (6 to 8 tracks) ***same
[4] WWinds (14 or more tracks) ***same
[5] Percussion (16 tracks) ***same
[6,7,8,9] - what ever seems to be needed on the fly ... duplicates of smaller string sections etc.
[0] "The Loading Dock" - where all instance of Kontakt are open and visible along with any other VSTi so I can
watch them load before I start hitting the space bar.

No problem knowing where I'm at in PRV. I mark the arrangement with markers and *always* record midi in PRV,
and always Sound on Sound and *never* comping.

So, I've very used to a complex detailed layout and would suffer if simplicity is introduced at the expence of lost functionality.
No big deal at this point. 2017.01 is great for me.

Seems like the Filtering function in the re-designed PRV is at least part of the way to where you want to end up, and the rest could be covered by having a Track Manager sync button for PRV in addition to the one of the Console.
 
If that would indeed do what you want, it doesn't sound like it would be too hard to do from a dev standpoint (not that I know anything about code).