------By chance when you clicked "submit reply" to submit your post did you have to sign back into the site?
Often I've clicked the "submit reply" button then had to sign back into the site. Somewhere in between my post and signing back into the site my posts got lost and never posted.
If this is what happened, in the future back click to your post once you are asked to sign back in, then copy your post because chances are pretty good your post won't show up--I don't know why it does this.
Then look on the thread to see if your it showed up. If does not appear then re-post your copied message/post by pasting it in the message/post box and clicking "submit reply" (as you did the first time).