Interesting, this was in a discussion here in the forum, since the software doesn't have the feature of removing certain words, it couldn't have been the forum software. I also tried it in preview and the word doesn't get removed there. So that pretty much rules out the software in my mind.
It now seems that the most likely reason is that I actually didn't type the word and only read it into the expression in my mind as a mental fill in the blanks while proofreading my post. Because it was a swear word, I just assumed that the word had been edited out or deleted, when it was actually just a normal typo. I find that often happens when the missing word either ends or begins a line. Your brain just fills it in when it reaches the beginning of the next line.