mcedit undo and warning

[d255]

Hello!

It looks like a bug for me.
In mcedit I have next warning when remove block of text (when length
is large than 16384): "Block is large, you may not be able to undo
this action"

But actually I can undo only when remove block of text with length
less than 8190.

So, when I remove block of text where 8190 <= length <=16384 I don't
get any warning and can't undo this action.

What version of Midnight Commander is used?
GNU Midnight Commander 4.8.19
Built with GLib 2.50.3
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, ftpfs, sftpfs, fish, smbfs
Data types: char: 8; int: 32; long: 64; void *: 64; size_t: 64; off_t: 64;

What steps will reproduce the problem?

1. Create text file which contains 8190 - 16384 chars
2. Open file with mcedit
3. Select all chars
4. Press F8 to remove selected chars
5. Press ctrl+u to undo "delete action"

What is the expected output?
Removed chars should be in their places or when F8 has been pressed the warning message should be appeared

What do you see instead?
Can't undo delete action. No any warning message