Blogger recently installed an automatic comment spam filter. Unfortunately it doesn't work all that well, and frequently puts a comment in quarantaine which isn't spam at all. The comment doesn't appear on the blog until I check the blog and mark the comment as "not spam". There isn't even a notification, neither to me or the commenter, that the comment got caught in the spam filter. And worst of all, the spam filter cannot be turned off.
Also the new system apparently still has a few bugs, giving out error messages when a comment is posted, making it look like the comment hasn't arrived, when in fact it has. As a result of the spam filter and the bugs I now frequently get double, triple, or quadruple comments from people frustrated they don't see their comment on my site right when they wrote it.
Please be patient, there isn't much I can do about it except for "teaching" the spam filter what comments are not spam. If you get an error message, refresh the site instead of reposting. And if you still created multiple posts, please delete the extra copies.