Nearly a week ago, my Movable Type installation suddenly informed me that I needed to upgrade it.
This was kind of mysterious, since I hadn't installed anything new. But I did a database backup, and then clicked the Upgrade button, figuring it couldn't hurt.
It ran for a few minutes, and then finished successfully.
And I looked at my blog and saw that all the right-side sidebars had disappeared.
It didn't take long to track down the problem: the upgrade had deleted the templates that created those sidebars.
So I restored the database from the backup. And got the upgrade message again. And discovered that I couldn't get to the MT interface (to do things like posting entries or managing comments) without going through the upgrade process first.
I filed a ticket with MT support. (I don't run into MT problems very often, but on the rare occasions when I did run into problems during my free-MT3-support period, it was very useful to be able to file tickets, so I decided to pay for support after upgrading to MT4.) They were as remarkably fast to respond as usual, but it took several exchanges to get the info I needed.
Turned out there was no way to disable the upgrade process. But the support guy suggested that I could back up just the mt_template table (which stores the templates), run the upgrade, and then restore just that one table.
So tonight I did that. With some trepidation; I'm a little worried that that means my templates are now out of sync with some version of some of the code, somehow. But everything seems to have worked--I did a mysqldump of just that table, changed the name of that mysqldump file to be sure not to overwrite it later, then ran the upgrade, checked to make sure the sidebars were in fact gone, did another mysqldump of the new mt_template table (to a new filename) just in case, and used the mysql command to restore the mt_template table from before the upgrade. And voila! Everything appears to be working.
I'm still a little hesitant to trust that everything works; hence this test entry. And I'm still kind of concerned, because this "upgrade" thing happened completely out of the blue, and the support people didn't seem to know why, so it could happen again at any time. The only thing I have installed other than the basic MT4.23 installation is Link Roller; I'll be sad if it turns out that's causing random upgrade-needed events. (But it had been running for over a week without any problems, so it seems unlikely that that would be the problem.)
Anyway. Keeping my fingers crossed that it was just some kind of weird fluke and everything will now work properly. We'll see.
And I'll try to remember to do more-frequent-than-usual database backups for a while, just in case.