Okay, trying to be more specific.

Bearing in mind that I don’t really understand any of this stuff, this is what phpinfo gives:
PHP 5.1.2
Apache Version: Apache/2.0.58 (Unix) mod_ssl/2.0.58 OpenSSL/0.9.8d DAV/2 PHP/5.1.2 mod_jk2/2.0.2
MySQL 4.0.18
Plus loads of other info that means nothing to me...
MODx 0.9.6.1 rev 3118 (although it was also a problem on 0.9.6).
In terms of browsers:
Firefox 2.0.0.11 on Windows XP
Firefox 2.0.0.11 and Safari 2.0.4 on Mac OS X
(Same problems for all these browsers.)
So, what’s happening is that, as others have said, TV values are not being saved in some, apparently-random circumstances, when entered through the manager. Sometimes this is when auto-complete takes over, but it also happens when I just enter a value in certain TVs. For me, this has happened for plain-text fields and for dropdown menus, although removing the default value from the dropdown seemed to help. It’s never happened to me with a rich-text TV. Using quick edit always solves the problem.
I haven’t tried the hack that ZAP suggested on manager/processors/save_content.processor.php, because that seemed to be referring to a previous release, and I’m not confident enough that I’m not going to screw things up.
I’m not sure I’m adding anything new here to what everyone else is saying, and if it’s going to work fine in 0.9.7, I can probably deal with using quick edit.