I seem to have resolved the problem regarding table formatting.
On another page I had used the following tags to put some text in a code block:
<pre><code>
...
</code></pre>
I looked at the page a few minutes ago and noticed that the tags were visible on the live page. Since editing that page last, I changed some configuration settings while attempting to get the table formatting to work. Specifically, I enabled all of the options in the Markdown settings.
One of these was “Escape markup,” which I figured caused all HTML markup on pages to be escaped and appear as text. I disabled that, but left Markdown extras enabled, and the table now has the correct formatting.
Markdown configuration options:
The table formatting problem has been resolved with one of the previously mentioned work-arounds (linked above).
Now, if only I could resolve the navigation menu problem regarding linkable menu objects, I’d be all set.