Pandoc recognizes an abbreviation and inserts a nonbreaking
space (among other things, this prevents a sentence-ending
space from being inserted in LaTeX output).

```
% pandoc -t native
Mr. Bob
^D
[ Para [ Str "Mr.\160Bob" ] ]
```

If you don't want this to happen you can escape the period:

```
% pandoc -t native
Hi Mr\. Bob
^D
[ Para [ Str "Hi" , Space , Str "Mr." , Space , Str "Bob" ]
]
```