Without knowing what you said in the feedback it's impossible to say why the comment (but not the red dot) has been removed.
The most common reasons are that it mentions an eBay or PayPal case, or the police, or contains profanity. However, feedback can also be removed for other reasons, for example where a buyer demands something that wasn't part of the original transaction.
For further information, see eBay's member to member contact policy: http://pages.ebay.co.uk/help/policies/rfe-spam-ov.html
