I ran into something today -- it's not quite a bug; more of an "ugly." In some situations, chord names collide with the span bar of a Grand or Piano Staff. Here is an example:
\version "2.25.13" \score { \new GrandStaff << \new Staff \relative { c''4 c c c | c c c c } \new ChordNames \chordmode { c2. q8. des16:maj9 | q1 } \new Staff { \improvisationOn b'4 4 4 8. 16~ | 4 4 4 4 } >> } -- Knute Snortum