i am having this issue with my thunderbolt.
i was using smart keyboard with the autocorrect turned off (this becomes important later). the words would just appear once in a while. it would happen in gchat and in text messaging. i would type something, press enter or send and then the very next thing i typed would have the last word i typed from the previous message appended to it.
example:
hi i have an android phone (press send)
phonei don't know why the last word i type reappears.
end example.
i thought it might be smart keyboard since it never did this before i started using smart keyboard.
i switched back to the factory keyboard.
it recently started happening again with the factory keyboard with the autocorrect turned on (i used to never have autocorrect turned on but i was convinced to use it).
what happens is the autocorrect bar that pops up will linger after i have pressed send. if i type fast enough after pressing send it will append the last word typed (via autocorrect) into the text field. this only happens once in a while, i presume when autocorrect is running slowly or i have done something to make the typing input functions on the phone run slowly. i don't know what it takes to produce this problem but it is very evident when it happens. i hypothesize that the exact same thing was happening when i was using smart keyboard, however since i had the autocorrect disabled i would never see the lingering autocorrect bar.
i'm not sure if this hypothesis is correct, but the effect is the same for both situation, whatever the explanation really is.