It's 11:27pm UK time and this has taken about 90 minutes to whittle down and isolate so I have not had time to research further.
SYMPTON: Entering a blog post with PHP code causes the whole thing to be ditched and an empty node/blog/add page to be presented again when certain content is added.
CAUSE: I have narrowed it down to this in my blog post,
$ctx = stream_context_create($params);
$fp = fopen($url, 'rb', false, $ctx);
fpassthru($fp);
As it turns out, it doesn't matter what input filter is used or whether it is an article, basic page, blog post etc, the fault was apparent in most of the combinations I tried. I thought it was initially the SyntaxHighlighter module but it still happened after turning that off.
By entering the code like so,
$ctx = stream_context_create($params);
$fp = fope n($url, 'rb', false, $ctx);
fpassthr u($fp);
I defeated the bug. Note the space character between the e and n of fopen() and the r and u of fpassthrough().
MYSTERY: How is it that I am able to enter it on the Drupal forum but not on my site? LOL As I was entering this post I suddenly wondered if the bug would be present here too but it seems to be fine so what version of Drupal is this site running ?
Now I am really confused!!!