My System Folder Format for 'This PC' is stock, and my User Default is stock with one column added.
When getting applied to 'This PC', Set FORMAT doesn't act as usual:
Set FORMAT=!default seems to apply the User Default Format.Set FORMAT=!folder applies the correct System Folder Format, but switches to a variation of the format when applied a second time.If you want to try it for yourself, here's the toolbar: 49297.dop
Not sure #1 is wrong, it's just that most columns don't apply to This PC.
#2 seems to be a bug relating to the "Add Group column automatically when file display is grouped" option, which I assume you have turned on. If the group column was added automatically and then Set FORMAT changes the format and leaves grouping turned on, the group column gets removed again. That'll be fixed in the next beta.
That is right, but shouldn't Set FORMAT=!default apply the System Folder Format for 'This PC' instead of the User Default?
#2 has been partially fixed by 13.3.1 
When duplicating the 'This PC' tab, the Group column gets removed, and Set FORMAT=!folder is unable to apply the original format.
Yes, I have.
Fixed in 13.3.2.
Going to 'This PC' via the /mycomputer alias removes the Group column. This time Set FORMAT=!folder can apply the original format.
I think this is working correctly now, but please let us know if I'm wrong!
This still happens when running GO PATH=/mycomputer and navigating to it via the Folder Tree.
Does the saved format for the folder include the Group column?
The option to automatically add the Group column is mainly for when doing ad-hoc grouping (although it can affect some other actions). Folder formats can still include or exclude the Group column while using grouping, whether the option is on or off; it won't force the column to be there if the format specifies otherwise (until you then do a grouping operation manually).