This is absolutely intentional. The default way of writing posts is using Markdown. If you decide to handcraft your HTML, we assume that you know what you're doing, and thus preserve any HTML tags you write; after all, you'll have a reason for not using Markdown (and bolding of code is pretty much the only use case I can think of).
So if you insist on writing your own HTML for a code block, you have commit to this decision all the way, and
< escape your tags if you want them to be visible.
As a side note: Code blocks on this particular site seem to be of limited use to me anyway. I know there are people who like to use code spans (
in `backticks`) as a way of emphasizing text (I noticed you have been doing it in a few places); that's hardly the intention of code spans, and usually comes at the cost of legibitlity.