Linux container disk usage does not make any sense


This might be a newbie question, but I could not find anything that makes any sense to me regarding the df command in a Linux container (Windows Docker 18.06.1-ce-win73 (19507)). For instance, I ran this on my SVN server container I get this:

/ # df -h /home
Filesystem Size Used Available Use% Mounted on
none 17.9G 17.7G 0 100% /
/ # df /home
Filesystem 1K-blocks Used Available Use% Mounted on
none 18745336 18552348 0 100% /

if it is 100% used then I should not be able to create any files on this /home directory,
but I can do this.

Can anyone clarify this mystery?