Spacing problems with triplets

[Tim McNamara]

Occasionally LilyPond will render triplets in an ungraceful manner:

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And

PastedGraphic-3.pdf
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All the quarter note triplets in the piece which are not under a volta bracket 
are rendered with nice, attractive spacing.  I have seen this before and cannot 
recall if the problem always occurs under a volta bracket.  Is this a bug?  
This is with 2.16.2, FWIW.