Vertical alignment of Chords - Feature / Bug???

[Simon J Mackenzie]

Hi
Could people please have a look at the PDF at the following link.

Note the positioning of the sixth and seventh chord in this dummy music sheet and compare their placement with that of the subsequent chords on the sheet. Is this normal behavior or a potential bug in the positioning routines for chord placement?

http://smack.fastmail.fm/LuaMusicBook.pdf

If this is not a bug does anyone have any idea how this sort of behavior can be prevented automagically?

Cheers
Simon