Richard, I would encourage you to contact our technical support team to address this issue. Likely, there is either an issue with the posting options in the browser, or browser version you are using, OR, there is a technical issue that we would love to work with you to investigate and get resolved as quickly as possible.
You can select the 'Sports Help' option on the right of this page, under the Help Resources box, and then select 'Contact Yahoo!' on the right of the page that loads. Please include details like the league ID# and your team name, where you are seeing the posts removed from, and the steps taken when you experience this issue.
We look forward to hearing from you, and investigating this issue!