Learn English – What are some examples of awkward sounding but grammatically correct sentences

Here is how the example sentences are grammatical:

• The old man the boats.
  The old [people] [man/serve on] the boats

• While Anna dressed the baby spit up on the bed.
  While Anna [got] dressed, the baby spit up on the bed.

• The man returned to his house was happy.
  The man [who was returned to his house] was happy.

• Fat people eat accumulates.
  [The fat that people eat] accumulates

• She told me a little white lie will come back to haunt me.
  She told me [that] [a little white lie will come back to haunt me].

• We painted the wall with cracks.
  We painted the wall [that has] cracks.

In:

In Latin, when a group of males and females is combined, the neutral plural form is not used, but rather the masculine is.

'but rather' is perfectly fine and a good alternative to:

In Latin, when a group of males and females is combined, the neutral plural form is not used; rather the masculine is.

'Rather' is like 'instead'; using 'but' allows it in one conjoined sentence rather than a separate one.