Incorrectly wrapped long utf8 PS1

[galtgendo]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: x86_64-pc-linux-gnu-gcc
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' 
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-pc-linux-gnu' 
-DCONF_VENDOR='pc' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash' -DSHELL 
-DHAVE_CONFIG_H   -I. -I./include -I. -I./include -I./lib  
-DDEFAULT_PATH_VALUE='/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin'
 -DSTANDARD_UTILS_PATH='/bin:/usr/bin:/sbin:/usr/sbin' 
-DSYS_BASHRC='/etc/bash/bashrc' -DSYS_BASH_LOGOUT='/etc/bash/bash_logout' 
-DNON_INTERACTIVE_LOGIN_SHELLS -DSSH_SOURCE_BASHRC -O2 -g -march=core2 
-mtune=core2 -pipe -Wno-parentheses -Wno-format-security
uname output: Linux blackspire2 4.4.39-gentoo #1 SMP PREEMPT Sat Jan 14 
12:21:50 CET 2017 x86_64 Intel(R) Core(TM) i3-2120 CPU @ 3.30GHz GenuineIntel 
GNU/Linux
Machine Type: x86_64-pc-linux-gnu

Bash Version: 4.4
Patch Level: 12
Release Status: release

Description:
        A detailed report is at 
https://bugzilla.gnome.org/show_bug.cgi?id=787157.
        Initially, I thought it was a vte bug, but there it was established 
it's a problem in bash. The report was made with bash 4.3, but with 4.4, while 
there's an improvement (no longer breaks line inside utf8 sequence; though 
during retesting I think I've seen it truncate PS1 in the middle of the 
finishing escape sequence once, but wasn't looking at that then, so don't 
recall exact circumstances), the oddities in wrapping / cursor movement remain. 
Pure ASCII paths seem unaffected.

Repeat-By:
        See the gnome bug.