Programming error: unknown avoidance type

[Nick Payne]

I have a two page guitar score that had all its notes complete, and was
going through adding barring, faking the barring indications with square
arpeggio brackets in a voice with transparent noteheads, stems, accidentals,
dots, etc. Anyway, after adding half a dozen of these brackets, I added one
more and suddenly got about 800 of these 

Programming error: unknown avoidance type
Continuing, cross fingers

errors showing up in the console output every time I build the score. The
PDF output still looks fine. I searched the documentation and mailing list
archives and didn't find any mention of this error...

Nick