Slope chart labels are sometimes in the wrong order when values are very close together

[jtrim-ons]

e.g. right-hand labels here.

data.csv:

name,leftValue,rightValue,leftRank,rightRank,leftCustomRank,rightCustomRank
France,100,690,100,690,4,4
Japan,2923,696,2923,696,1,1
Cayman Islands,179,694,179,694,3,2
Jersey,710,692,710,692,2,3

Sometimes this problem only shows up in Firefox, and sometimes in both Firefox and Chrome.

The problem seems to be in the arrangeLabels function, where labels can be moved out of order.