The example below shows the issue. The mid-bar line with a \break does not show the bar number at the beginning of the next line - I would expect '2'. A \break at the end of a bar gives the expected result.
Also, the commented out line doesn't compile, and I can't see why, so can't see if it would make a difference. I cut-and-pasted the vector from the manual, but that's what the complier seems to be complaining about.