Sorry for all the consecutive posts. But this will be my last here.
I was correct about the problem being in relation to the BBCode parser. This parser is, in some way, bugged. Where can I file a bug?
I have tried several ways of rewriting the functions that evoke the SSHTMLBBCode class methods without any resolution. I am not going to spend any more time debugging someone else's code. I have opted for HTML, as I prefer to use that in my blog over BBCode anyway. This workaround was revealed to me by the very helpful community member who replied to the question located here: http://www.silverstripe.org/blog-module-forum/show/251397.
In /blog/templates/Includes/BlogSummary.ss, I replaced
... with ...
This circumvents invoking the FirstParagraph function in /blog/code/BlogEntry.php, which calls the BBCode parser functions. It is a workaround because I cannot use BBCode, but I prefer HTML anyways (fortunately). It will probably need to be applied to other template or includes (.ss) pages as well, if the call for BBCode-evoking functions such as FirstParagraph.
I would be very interested in discovering why the BBCode parser is acting up like this, and (apparently) only for some people. It required a lot more work to diagnose the problem than it should have, as there are no errors output by this parser, which is a real problem. Can someone please point me to where I can file a bug report? This has to do with Sapphire and the PEAR BBCode parser class; it is not related to the blog module directly.