I'm not sure what to say about this. I'm not experiencing this glitch in Konversation, Opera or Konqueror, only in Konsole and Vim-qt. Sometimes, if I switch back and forth between workspaces (XMonad), the line I'm typing on in Konsole will display the entirety of the characters - and if I insert text before the characters the lower parts of them will be stuck in their original position.
I'm using a patched version of the font for the Powerline plugin, but using the original version makes no (visible) difference.
Also, as far as I know, it's only font size 14 that has these issues.