It's like getting audited, Tom!
If it happens once, it's likely to happen again. With all the programming and barrage of invasive advertising on FB, it's highly likely they're monitoring your posts on a second by second basis.
There is no privacy on FB, nothing belongs to the poster once it's posted and takes months (if ever) to rid their servers of information you've posted. It's Big Brother personified!
Now you see why I don't post much on my own wall, don't keep pictures long and don't "like" much...
If not for keeping in touch with people in MI that mean a great deal to me, I'd not bother...