Missing posts are most likely a result of it being a repeated post or it went against the guiidelines some how. I think mylot is becoming a bit more picky with the posts because the population is growing so rapidly here and a lot of people are spamming.
I think it happens when you refer somebody and he comes back and start responding to your questions.
This is to prevent cheating incase your questions remain unanswered and you come back to liven the thread.
A few reasons I think. Guidlines, short yes or no, or just a glitch. I have lost over 100 posts. Sometimes it goes backwards. It's very fustrating. I have emailed MyLot, but they have never responded to me.