When using SSH (bash) on Windows 10, Local 5.6.8+4514 (and earlier), I get the following error when using a wp-cli command that has quoted strings with spaces:
$ wp scaffold child-theme providence --parent_theme=chaplin --theme_name="This has spaces in it" --activate
'C:\Program' is not recognized as an internal or external command,
operable program or batch file.
This issue occurs using both double and single quotes. Removing the offending arguments (--theme_name in the example) resolves the issue.