Some Barcodes intervals not drawn parallel after keying in the position of slice line

[mlesnick]

The bug arises both on Linux and Mac OSX. Until now, we haven't keyed in the position of the slice line so often, so perhaps it's not surprising that we never noticed this bug. I am making figures for a paper and so I want to key in nice round values for the slice line parameters. (Fortunately, for my immediate application, I can just use slightly different parameters.)