FYI, this bug also happens on volta brackets that continue or start at a new
system. The beginning of the volta bracket is "pushed" to the right by the
mark. This is exasperated by the fact that very often it is necessary to
put a "To CODA" mark at the beginning of first endings. In this very
frequent (pop music) case the volta bracket correctly ignores the coda mark
if it is starting in mid-system but if the coda mark and volta start happen
to occur at the beginning of a new system, the coda is pushing the volta
around so it looks like the alternate ending is beginning in mid-measure.
I've been coding around this by forcing my voltas to never start a system,
as I did not realize it was a bug, so feel free to add this too.