There's a fix for this annoying layout problem available from Blogger Buzz but I can't try it because I still haven't solved my modem thing and my stylesheet is not embedded in the top of the blogger template but is a seperate CSS file.   it didn't work on my template. The one kindly linked to in the comments to this post did, however, so at least the scrolling is solved.

I also don't know if their fix will The fix doesn't resolve the problem of blogger no longer formatting paragraphs as paragraphs unless I manually type in some html <p> tags. I tried possibly even   leaving them open - i.e. without a closing </p> tag -   to get the rest of the posts fixed  but it didn't solve it and is bad naughty html anyway. I'll be damned if I go through manually coding every damn frikkin' post because blogger have totally screwed up by introducing new code which doesn't work. If the function has ballsed things up then they should:
a) take it back out,
b) fix it
rather than expect everyone to scramble around fucking up good html/css because of their bad implementation.

Ah, well, at least I have a modem at home again.