[ldolse]

You could also try enabling preprocessing under structure detection for this sort of scenario. Aside from fixing hard line breaks it also looks for common chapter headings which aren't properly marked up and wraps them in <h2> tags. The scenario you're describing here is covered. In this particular case the default chapter detection xpath would work when combined with the preprocess option.

Edit - just saw this was epub source - in that case it's more complicated as epub is assumed to already be 'good'. You'd need to rename the file from .epub to .zip and add a new format as zipped html to be able to use the preprocess option. In most cases where this occurs it would be worth the effort though, since the file was more than likely originally converted from Lit to epub by someone else using an older version of Calibre, and since they didn't mark it up correctly it means that there are probably also page breaks scattered randomly throughout the book. I'd convert from zip back to epub using Calibre, then edit in Sigil and re-join the broken chapters together before trying to convert to mobi.