It's not really a bug if we weren't using or expecting HTML in that context. When it comes to translations, the rule of thumb is that if the English version doesn't use HTML, a translation shouldn't because we can't guarantee it'll work. It's more difficult when it comes to add-ons, but if you try to use HTML in a place we're not expecting it, then that would generally be how it's designed.
We'd need specific reproduction steps, but it's unlikely a particular context would change at this point.
Just to add a little twist, if you format the variable using standard \r\n, the system also completely strips that formatting making it impossible to have line feeds in a phrase variable.
Indeed, the issue here is that you're trying to pass HTML in a parameter. Parameters are HTML escaped by default. Without this, you'd basically have XSSes everywhere. The "false" mentioned by @Arty disables the escaping, which means you'd be responsible for it (escaping the parts other than the HTML you're trying to inject).