Hmm... that's odd. I always type my BBCode by hand, not use the stuff in the scroll-down lists and stuff. If you don't know about the coding, click on the hyperlink from the "BBCode" is on stuff in the options right below the text box of your post. This will open up a new window with BBCode help. That should work. 
As for posts disappearing, you'd have to talk to one of the current moderators or admins about that. They might know what's going on, even when the rest of us are left in the dark, so to speak. 
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Itaque incipet.
All that glitters is not gold but at least it contains free electrons.