I have the problem with not working subshell on mcedit and mcview of Midnight Commander package on all my Ubuntu systems.
When I in mc file manager, ctrl+o drops me to the full-featured shell (bash), so I can see previous shell output, type and execute commands.
But when I on mcedit or mcview application, ctrl+o only shows me previous shell output. So I see black sceen with provious output but without cursor.
And when I try to type anything on this screen, I goes back to mcview or mcedit.
Problem is reproducible on normal user, on sudo and on root user too.
mcedit and other apps compiled "With subshell support as default", here is output
$ mcedit -V
GNU Midnight Commander 4.8.12
Built with GLib 2.40.0
Using the S-Lang library with terminfo database
With builtin Editor
With subshell support as default
With support for background operations
With mouse support on xterm and Linux console
With support for X11 events
With internationalization support
With multiple codepages support
Virtual File Systems: cpiofs, tarfs, sfs, extfs, ext2undelfs, ftpfs, sftpfs, fish
Data types: char: 8; int: 32; long: 64; void *: 64; size_t: 64; off_t: 64;
How can I debug where is the problem and fix it?
I don't know how you could debug this further, but there is a solution mentioned on MC bug tracker page. Go to Options/Configuration and enable Use internal edit.
It has been troubling me much also :)