"invalid argument" error while saving

[SunflowerFuchs]

Description of the problem or steps to reproduce

• Open a file for the first time with sudo micro
• Open the file a second time, but without sudo this time
• Try to save

Specifications

When saving a file, it displayed an error "invalid argument" (the file still gets saved).
I managed to pinpoint it to being due to the buffer file being owned by root, which happens when you open a file for the first time with sudo.

Commit hash: af520cf
OS: Ubuntu 16.01
Terminal: gnome-terminal with zsh