I can see the 'last paths' used in file open functions for save book, insert link in comments, add books etc. And they get updated if I save, insert or add books to/from another other location.
If they all work across sessions then why shouldn't the ebook-edit save copy function work. Nothing apart from calibre reads or writes to the dynamic.pickle
Just started the editor direct via Windows Open With, calibre was not running
Did a save copy, it offered my home directory,
But I selected E:\Calibre Libraries\Editing\SaveCopies the save was fine
Closed the editor and opened another epub
Did a save copy, it offered E:\Calibre Librar...
So I started calibre and started editor from it, did a save copy and it offered E:\Calibre Librar..., but I saved to the Desktop. Restarted calibre, edited another book - save copy offered E:\Calibre Librar..., not Desktop
Looks to me like the 64bit version of calibre.exe is blocking the 64bit version of ebook-edit.exe writing to dynamic.pickle
BR