Left-hand end of tuplet bracket sometimes wrong

[Paul Hodges]

Both Ross (p161) and Gould (p195) are completely clear when they say that the left hand end of a tuplet bracket aligns with the left-hand side of the first note.

However, LilyPond doesn't always do this - instead, if the first note has an up-stem, the bracket is aligned with the stem instead.

Is there a reason for this?  And is there a way to correct this globally, or do I have to tweak shorten-pair for each affected instance?

Paul