( FIXED )
We are currently investigating reports from users of certain browsers, that the Subject column in Web Mail disappears or the messages can't be clicked on. Usually what happens is that only white space is seen in the subject column.
These reports seem to be occurring on various flavors of mozilla-based browsers only. These include Netscape, Firefox pre-2.0 versions only, and generic Mozilla browsers from mozilla.org. The problem doesn't ever seem to occur on Internet Explorer or Firefox 2.0 or Safari or Opera.
The problem seems to mostly occur when there are many messages in a particular folder (hundreds). So moving messages out of your Inbox frequently will help.
If you are using Firefox 1.5, an upgrade to version 2.0 fixes the trouble for most users. Go to http://www.mozilla.com/en-US/
I'll have more news when we find the cause and fix it.
WORKAROUND for Netscape 8.x users: click View / Rendering Engine and set it to "Display Like Internet Explorer". Some users report this fixes the problem. Thanks to user Robert Meintzer for the tip.
If you are still using an older version of Netscape, get the newest 8.1.2 version here.
UPDATE - Some Mozilla users report that lowering the "messages-per-page" setting in Preferences / Web Mail Options, to 10 or 20, fixes the problem for them.