Autocorrect changing word at beginning of sentence

C

CAW

I have noticed over the last couple of months that the autocorrect on my Galaxy Note 3 has started correcting the first word I type in a sentence - example: I tried to start a sentence with 'Unless' it changed it to 'Ness'. It does it with the most common words, like 'what', 'if', 'why' etc.
There seems to be no reason for the autocorrect. The words are not misspelled and are sometimes changed to things that make no sense (see above example)
It does seem to be more prevalent in WhatsApp than anything else.
Has anyone else noticed this?