Since I knew I would have problems accessing internet for a few days I downloaded all boundaries in Minas Gerais and did a little tidying on the border relations (created micro and meso region borders mainly), I discovered that there is a gap in the border between Ouro Preto and Mariana. Downloading the area with the gap, and there is certainly a gap, nothing connects or almost connects the two sides of the gaping boundary.

Somebody with access to the source data that can help fill in the gap?