UPDATE: I've changed the date/times of the posts back to their originals now. Thanks to Spiderzilla I had taken a local backup of my site recently so I could pinpoint the original date/times from the copy of my blog on my hard drive.
FURTHER UPDATE: nope, it's fine now, no change at all in the original date/time when I edited and republished this post. So there must have been something odd at Blogger's end this morning/early afternoon. I can't think of any other explanation for this. I do know what I'm doing when editing posts, I've done it often enough! Thanks to Kirk for the comment explaining the redirect on New Blogger (good stuff that, thank you Team Blogger, very helpful); still learning stuff about New Blogger all the time, and still a long way to go!
OK, something weird is going on.
Today, when I edited some old posts to update some links in them, Blogger republished them dated TODAY not the original date. The Keep Current Time script is not meant to affect old posts, i.e. when editing old posts the box is not ticked, and I am very sure they're still not ticked (I checked on one of them before hitting Publish, too). Could be a conflict with the "Publish Now" script which I was trying out but had recently disabled.
And yet you can still get to the original posts if you go to the original direct URL (e.g. this Haloscan one and this flag bookmarklet one) - the original links are redirecting them to today's version, somehow. So I suspect it's New Blogger rather than the script not "taking". What gives?
I don't know what's up but please ignore my other "posts" today, as they're edits of old ones. I'm leaving them for now as I have to go out as I'm going to be an hour and a half late to a do! I'll have to redate them and hope that'll work. If only I can remember their original dates... well months will have to do, I can get that from links to them elsewhere.