tonight i finally got around to looking at the code to see what was wrong. blogger was inserting <div style="clear:both;"></div> at the end of each post, right before the haloscan comment code. there was no mention of it in the official blogger help, but i knew i couldn't be the only one experiencing this problem, out of however many hundreds of thousands of blogger users.
google quickly turned up this bloggerforum thread, which led to a suggested css fix on this thread. the fix used css to disable the "clear:both" part of those tags... but that wouldn't help for my template, because the problem there was that the <div> itself was a block element, and the fact that it was there at all was breaking the layout. fortunately, it turns out blogger now has a fix, and an explanation (emphasis mine):
In order to provide the layout options in our newly released Blogger Images we had to wrap all posts in a <div clear:both> tag. For some users this resulted in template formatting issues (even without uploading images). So today we introduced a new setting to suppress that markup.
Please note that suppressing the markup will result in layout problems when using left or right alignment for images. You should only change this setting if you are currently having trouble with normal posts.
emphasis mine. the new setting stops blogger from inserting those divs, fixing the problem with my layout. so that's that. however...
you'll notice that bobby vomit's blawg never experienced this problem. that's because that he hasn't posted in a couple weeks. if he ever posts again and republishes the blawg, the same thing will happen (unless we turn on that setting).
i don't know if i'll ever use the new layouts for blogger images. but maybe i will want to sometime. or maybe bobby vomit will, as he does post a lot of images. if we do, the current template/setting will fuck it up. maybe i should redesign the comment footers?
also, haloscan comments aren't totally reliable. sometimes haloscan goes down and they temporarily disappear. sometimes the number of comments doesn't update right away. and virago notes that she lost an entire comment somewhere in the ether. there's a trick here to switch over to blogger's built-in commenting system without losing your old non-blogger comments. that's kind of tempting. and blogger even has a new feature for pop-up comments like haloscan's.
in order to set that up i'd need to enable post pages. at first i was concerned that this would mess up any existing links to old blog entries, as post page archiving totally changes the way posts are archived and saved. but then i realized that as long as i don't delete those old files, the links should still work.
so... yeah. in the time i spent writing this post about changing to blogger comments, i could have actually changed to blogger comments. but if i do decide to do it, maybe i will soon. if you have an opinion, feel free to try leaving a haloscan comment. it works most of the time.