This thread is becoming a bit of catch-all. The OP was likely encountering a parsing problem in reading view and the rest is unrelated to their post but related to the title.
I would not say that Live Preview and Reading mode are very different, but there are differences.
Most of the differences are due to fact that Reading view contains the HTML output of the whole processed document whereas LP is, at its core, a plain text editor with enhancements to make it look-like the rendered document.
I think LP can be improved further, but there are both technical limits to what can be done and also design decision that we make.
For example, in markdown, extra lines in the source of the document are removed in the rendered HTML. If we were to remove/hide them from LP, we would introduce the problem of those lines being hard to discover in LP and also cause a jump in the document viewport when they are expanded.
Some problems are very hard. For example we spent a lot of time faking the list indentation in LP and it’s still not perfect.