:help autoformat
gives some useful hints:
- You need to properly define paragraphs. The simplest is paragraphs that are separated by a blank line. When there is no separating blank line, consider using the 'w' flag and adding a space at the end of each line in the paragraphs except the last one.
So, either :setlocal fo+=w
, or turn off autoformat (maybe only temporarily, with a quick toggle mapping).