I had found same problem. I had changed Permalink Entry URL structure. When I changed it back to archives/%id%-%title%.html, it works again.

I found the problem maybe caused by bbcode plugins.
If I delete bbcode plugins, the entry include links and image will display tags, and if I use bbcode plugins, the entry include links and image don't display tags.

I found a problem with Tagging of entries plugin, when I post new entry or edit entry, if the entry had a link or image, then this post can not display tags, if the entry is all text, the tags will display.
Anyone know this problem?
My test blog powered by Serendipity 1.0 and PHP 4.3.9, and the ...