This has already been reported at https://github.com/vim/vim/issues/2008
Thanks!
I use KDE, so added 'set term=konsole-256color' to my .vimrc file.
I see that I have in my .vimrc the following: if ($TERM!="") :set invttybuiltin term=$TERM endif
So I tried setting TERM to konsole-256color and it worked.
Thanks,
Frédéric