Hello Stephen, I am afraid it does not address the problem
Here is my scenario
I usually use my Macbook Pro in Camshell mode (with display lid closed) when I am in my office desk.
I have two 4k monitors hooked with my MBP (it pretty much gives you a desktop like scenario, because I hide by MBP under the table )
I have seven spaces in each monitor totalling 14 spaces and I have sync grids checked and also “Displays have separate Spaces” under Mission Control Preferences.
Here is the screen shot of my layout for both monitors
Now when I unplug my external monitors and work with my MBP display the layout automatically transforms to two row (this is expected, each row corresponds to spaces in external monitors when they were connected), and when I reconnect my monitors again the layout automatically gets restored with 7 spaces for each monitor like it were before I disconnected them.
The actual problem is that the first space from each monitor gets merged into single space, this makes only 13 spaces instead of actual 14. However OS X somehow seems to remember which window in the merged spaces belongs to which monitor (first space) so when I reconnect them they automatically gets moved to respective monitor (spaces) like how they were before.
Merging of spaces makes it difficult to navigate between the respective space from the monitors using up & down arrow. First row contain all the spaces of Monitor 1 but second row contains N - 1 (6 spaces) from monitor two, hence they loose the association.
This is how the layout looks after disconnecting monitors. I expect all the 14 spaces be there or atleast a empty space in the second row’s first position so the mapping between monitors are preserver when navigating using up & down arrow.