I've got almost the same question as the one here however the accepted solution is not working for me.
Whenever I type the word dont the google keyboard automatically corrects it to Dont (capitalizes the D). In the word suggestions it shows the correct auto correct don't to the right of the three suggestions above the keyboard. Additionally if i write dont at the start of a sentence the auto correct comes out as Don't which is correct. And finally lets say I type sont accidentally, the word does get auto corrected to don't, again correctly. So why the word dont auto corrects incorrectly I don't know.
As per the example question the accepted answer was to clear the data for the keyboard, which I have done, but it doesn't change this behaviour...This surely can't be default behaviour of the keyboard can it?
p.s. If it matters this is with the UK english keyboard on 4.4.2