The problem with this is that it does not quote < and & properly. This isn't normaly a problem, because PM allows you to use < many places, escaping it itself, and browsers will display &foo; as such if "foo" is not a known escape. (It's important to note that the former is an explicit action of PM, to allow people to right $x<42, <g> and other similar things without additional effort, whereas the later is a normal part of rendering HTML, so even when a UA recives an entity that it does not know, the user has a chance to guess at what it means from the mnemonic name.
However, try writing a block quote of & <b>this should not be bold</b>
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