This sounds like a separate problem from the one with replies you posted about on Community. I too have noticed that root posts are sometimes altered, after somebody replies, and I suspect a rogue filter in WordPress that's scrubbing somebody's idea of "wrong" HTML. For me it's most often losing an entire iframe, e.g. used to embed a YouTube video.

It may be scrubbing obsolete HTML, tags that are no longer officially canon (though browsers tend to be forgiving). You mention centering, and the old <center> tag is one of the ones no longer supported. The modern way is to use the 'style' attribute inside a tag. For an image, it would look like

<img src="" style="align:center;max-width:640px" >

(The max-width:640px clause is something I throw in to ensure wide images don't overflow the window and make text too wide to read.)

Moar info please.