Just after the word is changed the word which was before should appear in suggestion bubble - if you tap it just after the unexpected word's change, it will come back to the sentence. Did you try it?
For example:
You type "jumped". Probably in suggestions bubble you see the word "killed". Just after you enter space, the word "jumped" is replaced by "killed" (as it was the last suggestion of the program). In the same moment the word "jumped" replaces the word "killed" in suggestion bubble.
So, if you would like to have "jumped" in your text just tap on "jumped" in suggestion bubble and the word "killed" will be replaced back by "jumped".
Sorry if my explanation is too complex but I hope it will help you.
Good luck
