Markdown line breaking after a fullstop.

When typing a line of text that's not even long:

Expected: 

test. test. test. test. 

Actual:

test.
test.
test.
test.

This happens all when typing.

I found that only the first line break has to be manually entered, but the 2nd, 3rd, 4th and subsequent line breaks will be automatically created. These are my current settings:

I need a fix asap, it's so frustrating.