(Stick around for the third one, which explains why these are here.)
If the label for a post hasn't been used before but matches the start of a label that has been used before, typing the new label into the Labels for this post: text box, followed by a comma, inserts the existing label. For example, if you already have a post labelled foobar and you try to label a new post foo and baz by typing foo, baz into the text box, when typing the , Blogger will automatically complete foo to foobar. The work-around for this is to accept the incorrect label then use the arrow keys to delete the extra letters.
If a post begins with a block-level element (such as a list) rather than an inline-level element (such as
a) or text, Blogger adds an empty paragraph to the start of the post.
Blogger assumes you'll be writing unsemantic plain text, with paragraphs represented by double line breaks (which Blogger converts faithfully and unsemantically into
<br /><br />), so it adds an opening
<p>tag at the start of each post, in case someone tries to style paragraphs with CSS; when it comes across the list it closes the open paragraph, leading to an empty paragraph. This is just the tip of the iceberg when it comes to Blogger assuming, encouraging and even (occasionally) enforcing unsemantic, awful mark-up.
When I tried to report these as bugs using Blogger's bug-reporting page, I was presented with no text entry area of any sort. Silly Blogger.