FF changed my O date?

I've ovulated on day 14 the last 4 cycles Ive charted, with the exception of one cycle when I dont think I o'd at all, but FF thinks I might have on day 18. Anyway, Im on day 18 now, and just entered today's temp, and now FF has changed my O date to cd15. Why would it do that? Im very certain I o'd on day 14, because normally the day before I o i get cramps thats can last up to 2 hours.
I dont really think it will affect our chances of conceiving much this cycle, Im on a course of painkillers, anti biotics and anti inflammatories for another week, but Im just curious as to why FF would change its interpretation?

just a guess, but it looks like your temp rise on day 15 may not have actually been high enough, I felt certain that I O'd on day 14 of this cycle but then on day 18 my ovulation and coverlines disappeared, very annoying but better to have accurate information. Alternatively you can manually change your ovulation and coverline if you wish.

true, i guess FF knows what it is doing :)
Is it possible to move or remove coverlines all together? I had one month where I am certain i didnt O at all, the temps hardly raised, maybe 0.5C, and I had watery CM for over a week, but now it throws out all the data ie average O day, average cycle length etc

I think you can move/remove coverlines in the override section.

Thank you :)