Your top example is running with a non-Unicode locale (i.e. ASCII). Check your $LANG environment variable (try
export | grep LANG); you will most likely not find a
.UTF-8 suffix. Try adding it:
Your other example is running with a UTF-8 locale, which should be the default for recent shells. It seems
htop detects your locale and displays either ASCII or Unicode characters - so in the bottom picture, you get nice Unicode characters, while with ASCII you get some pretty makeshift ones. I'd suggest changing the locale of the top picture's machine to a Unicode one (see Locale - Debian Wiki).
If that doesn't work, it might be that your terminal emulator is the problem. The default encoding could be non-Unicode. Change the default encoding of your terminal emulator to UTF-8 (in
xfce4-terminal I found it in the Advanced tab). If you can't, it might be that your current font doesn't support Unicode: try changing your font to a Unicode one.
[Strangely, I found once I'd changed my locale to ASCII once in a shell session,
htop always displays the ASCII characters, even after changing it back. That might be your issue, if for some reason you are changing your locale in your shell occasionally.]