I've seen visual glitches like this for so long, I think they
might be more to do with Apple than with GNU-&-company.
I've applied all nine official patches thus-far to bash-3.2 and
the one official patch to readline-5.2, have pointed their
builds to use my build of ncurses-5.5+patches residing in
/usr/local, have the latest versions (some from cvs/svn) for
almost every other open source project (hundreds) I also put
into /usr/local including iconv/intl, gettext, etc.
I like to use hilighting for the bash prompt, and put the
settings in /etc/bashrc. I was using this one-line PS1 string:
PS1='\e[0;7m\h[\w]\u\$\e[0m '
but decided to start using a two-line string:
PS1='\e[0;7m\h[\w]\n\u\$\e[0m '
. ^^
so we could see long 'pwd's. ;)